Originally proposed by Xi'an Aircraft Factory in June 1970 as a 4-engined version of Xian H-6, design begun in February 1971 after the proposal was granted by the state. In 1973, People's Liberation Army Air Force (PLAAF) issued additional requirement of incorporating capability against sea targets, and formally joint the project. By the end of 1977, the first sample was completed and the maiden flight was followed in January 1978.
The aircraft was able to climb 40% faster than H-6, and the range is also increased by a third to 8,000 km. More weapons could be carried, including bombs of various sizes, sizing from 100 kg to the massive 9-ton ones. The bomb bay was sized at 8.6 meter x 1.8 meter x 2.72 meter, capable of holding a maximum of 18 tons of ordnance, i.e. 2 of the 9-ton bombs, though to achieve maximum range, the payload had to be greatly reduced to 7 tons. Nuclear bombs could also be carried, as well as anti-ship and land attack missiles, and in the latter configuration, a total 3 missiles are carried, one under each wing, and a third semi-buried in the bomb bay. The permanent weapon of the aircraft is a tail gun mount incorporating a twin 23 mm gun.
The crew totaled 6, seated in two separate pressurized compartments. Pilot/mission commander, co-pilot/flight engineer, navigator/observer, and bombardier/flight mechanic were seated in the forward pressurized compartment, while the electronics warfare/communication officer and tail gunner/assistant communication officer seated in the pressurized compartment in the rear. The avionics of the aircraft borrowed heavily from the reverse engineering similar American systems obtained from the downed Boeing B-52 and other American aircraft provided by North Vietnam during the Vietnam War.