China is trying to build its own jet engines.

[Swampy]

It can't do it, so it has to rely on Western and Russian jet engines. I didn't know that.

Actually, one of the challenges in the 1970's of building a cruise missile was to have a miniature jet engine, and that design was one of the major accomplishments of the time. Again, I didn't think about it until I read it somewhere.

[boxcar]

Engines

It was reported in November 2006 that a T/W=10 17,000 kilograms (37,000 lb) class turbofan (WS-15/"large thrust") was being developed for the J-20. One (#2001-01) prototype is fitted with AL-31F, the other (#2001–02) is fitted with the improved WS-10G with a new "stealth" nozzle possibly to reduce RCS and IR emission.[2]

The prototype could be powered by twin 32,000 pounds (15,000 kg) thrust Saturn 117S engines provided by Russia,[52] a sign of problems in the development of the aircraft, according to Pentagon spokesman Col. David Lapan.[53] Chinese sources have claimed that production aircraft will be powered by two 13,200 kilograms (29,000 lb)/WS-10 class high thrust turbofan engines fitted with Thrust Vector Controlled (TVC) nozzles, both made in China.[5] However Richard Aboulafia has said that the WS-10 engine has suffered catastrophic failures in flight.[54] The best estimates are that China will take five to ten years to perfect the fifth-generation jet engines needed for the J-20.[55] Production of the current J-20 prototypes appears to be hampered by the lack of engines to power the aircraft

(The J-20 weighs 70,000 lbs and therefore needs over 70,000 lbs of thrust. China has not meet this requirement so far).