6th institute of the Beijing Aerospace Propulsion Institute successfully conducted tests of the YF-79 engine pressure chamber on Dec 10 and Dec 17, 2021. The YF-79 is a 25 ton thrust LH2/LOX expander cycle engine use in CZ-9 third stage. It is a high performance, high reliability, variable thrust engine designed for multiple re-ignition. Used in CZ-9 for manned lunar mission, manned mars mission and other deep space mission. It has three times the thrust of the current upper stage engine YF-75D used in CZ-5. The Dec 10 test was conducted at 60% designed thrust, and the Dec 17 test was conducted at 100% of the designed thrust. Test data verified to meet the designed specification of the engine.