The J-20 has a long and wide fuselage, with the chiseled nose section and a frameless canopy resembling that of the F-22 Raptor. Immediately behind the cockpit are low observable intakes. All-moving canard surfaces with pronounced dihedral are placed behind the intake ramps, followed by leading edge extensions merging into delta wing with forward-swept trailing edges. The aft section features twin, outward canted all-moving fins, short but deep ventral strakes, and conventional round engine nozzles.
In one paper published on a Chinese aerodynamic journal, a designer of J-20 described high instability as an important design criterion for J-20. A canard is used to achieve sustained pitch authority at high angle of attack, as traditional tail-plane would start to lose effectiveness. This is because tail-plane would go into even higher angle-of-attack and stall, whereas canard can avoid this effect by deflecting to the same magnitude but opposite to the angle-of-attack. A canard configuration can also provide good supersonic performance, excellent supersonic and transonic turn performance, and improved short-field landing performance compared to the conventional design.
The same journal paper also explained how leading edge extensions and body lift are incorporated to enhance performance in a canard layout through interactions among vortices. One graph shows the configuration to generate 1.2 times the lift of an ordinary canard delta, and 1.8 times more lift than a pure delta configuration of similar size. This allows the use of a smaller wing, reducing supersonic aerodynamic drag without compromising transonic lift-to-drag ratio characteristics that are crucial to the aircraft's turn performance.
The production version of the J-20's is believed to be the WS-15, a turbofan engine currently under development. According to Global Security, the engine core, composed of high pressure compressors, the combustion chamber, and high pressure turbines were successfully tested in 2005. An image of the core appeared in the 2006 Zhuhai Air Show. Since 2012, China has reported numerous breakthroughs in development military turbofans and invested up to 20 billion US dollars in turbofan engine research and development. The J-20 has the potential to rivial the F-22A Raptor in performance once appropriate engines become available.
Western analyst believe that the current prototypes are powered by WS-10 or the AL-31F engine. China is a large importer of Russian-made jet engines, prompting rumors that China seeks to obtain AL-41 117S engines for the initial production of J-20 through Su-35 purchases. However, these rumors have since been denied by China, and were proven as false. It was also reported that Russia approached China in an unsuccessful bid to sell 117S engines during the 2012 Zhuhai Air Show.
The aircraft features a glass cockpit, with two main large color liquid crystal displays (LCD) situated side-by-side, three smaller auxiliary displays, and a wide-angle holographic head-up display (HUD).
A PLAAF Tupolev Tu-204 testbed aircraft was seen featuring a J-20 nose cone. It is believed to house the Type 1475 (KLJ-5) active electronically scanned array (AESA) radar with 1856 transmit/receive modules.
Prototype "2011" featured a revised nose section with elements resembling a IRST/EOTS system used to hunt low observable aircraft, and a metal finish that loosely reminds the radar absorbing Haze Paint first used on F-16s, and reportedly included sensor fusion technology.
The main weapon bay is capable of housing both short and long-range air-to-air missiles (AAM) (PL-9, PL-12C/D & PL-21).
Two smaller lateral weapon bays behind the air inlets are intended for short-range AAMs (PL-9). These bays allow closure of the bay doors prior to firing the missile, thus enhancing stealth.
No gun has yet been seen on any J-20 model and there have not been signs of provisions for one.
Analysts noted that J-20's nose and canopy use similar stealth shaping design as the F-22, yielding similar signature performance in a mature design at the front, while the aircraft's side and axi-symmetric engine nozzles may expose the aircraft to radar. One prototype has been powered by WS-10G engines equipped with a different jagged-edge nozzles and tiles for greater stealth.
Others have raised doubts about the use of canards on a low-observable design, stating that canards would guarantee radar detection and a compromise of stealth. However, canards and low-observability are not mutually exclusive designs. Northrop Grumman's proposal for the U.S Navy's Advanced Tactical Fighter (ATF) incorporated canards on a stealthy airframe. Lockheed Martin employed canards on a stealth airframe for the Joint Advanced Strike Technology (JAST) program during early development before dropping them due to complications with aircraft carrier recovery. McDonnell Douglas and NASA's X-36 featured canards and was considered to be extremely stealthy. Radar cross-section can be further reduced by controlling canard deflection through flight control software, as is done on the Eurofighter.
The diverterless supersonic inlet (DSI) enables an aircraft to reach Mach 2.0 with a simpler intake than traditionally required, and improves stealth performance by eliminating radar reflections between the diverter and the aircraft's skin. Analysts have noted that the J-20 DSI reduces the need for application of radar absorbent materials. Additionally, the "bump" surface reduces the engine's exposure to radar, significantly reducing a strong source of radar reflection.