On January 3, 2019, the Chang'e-4 probe successfully made a soft landing on the back of the moon, achieving the first human landing and exploration on the back of the moon, and the mission was a complete success. As a key subsystem of the probe, whether the Chang'e-4 power system can work reliably directly determines the success or failure of the Chang'e-4 mission. The power system provides the probe with attitude control thrust and orbit control thrust during the entire process of Earth-Moon transfer orbit flight, circumlunar orbit flight and landing flight, and provides precise power for the probe's lunar capture and soft landing on the back of the moon. The Chang'e-4 power system continuously outputs high-precision attitude control thrust and orbit control thrust from the probe's entry into orbit to the full cycle of soft landing. The Chang'e-4 power system began in 2015. After full testing and testing during the development process, the flight products were delivered to the probe in 2017 and the mission was completed in 2019. The main indicators of Chang'e-4's high-precision soft landing power technology are: (1) The structural mass of the power system is no more than 296kg;(2) the maximum propellant loading capacity is 2600kg;(3) 1 7500N orbit control engine is equipped, 16 150N attitude control engines and 12 10N attitude control engines;(4) The 7500N orbit control engine has continuous thrust variable capability, and the thrust deviation of the orbit control engine is not more than 2%. Chang'e-4 power technology adopts a constant-pressure extruded dual-component unified system. The pressurized gas is stored in 2 composite gas cylinders. The tanks are 4 identical metal diaphragm tanks. It is equipped with a 7500N variable thrust trajectory control engine and 28 attitude control engines. The attitude control engine has fault reconstruction capabilities. Chang'e-4 power technology has successfully completed the development, launch and flight test work, making outstanding contributions to my country's first successful lunar back soft landing flight test. The main technical innovations are as follows: (1) High-precision control and accurate prediction of engine thrust Thrust technology innovation: By accurately evaluating the specific impulse and characteristic length of the engine, using carbon fiber composite tank technology and composite transition joint throttle technology, high-precision attitude control and orbit control thrust are effectively provided, providing stable flight control and multiple times of the detector. Precise orbital changes and precise landing provide key guarantees. (2) Technological innovation in reliable locking and optimized drive control of stepping motor: LDquo; initial locking and optimized drive control strategy rdquo; is adopted to carry out variable thrust adjustment control. The variable thrust adjustment control during flight is reliable, accurate and fast, ensuring the detector's accurate landing. (3) Technological innovation in overpressure safety management of rail control pipelines: Through research on the mechanism and analysis of test laws of pressure and temperature changes of propellants in closed pipelines, a strategy for heating the engine injector and pipelines was formulated, and the model of ldquo; thermal control management + autonomous pressure relief management rdquo; is adopted for overpressure safety management in rail control pipelines, which greatly reduces the number of pressure relief actions of self-locking valves and improves the reliability and safety of the system. (4) Innovation in reliable passivation technology in relay mode: For the first time in China, passivation of residual propellants and pressurized gas has been completed reliably and safely in extraterrestrial objects and heaven and earth large delay relay mode, ensuring the safety of the detector after landing. (5) Innovation in engine quantitative polarity testing technology: Using ldquo; quantitative testing technology rdquo; that converts the measured into electrical signals, solves the problem of non-quantification in polarity testing and difficult data traceability. Chang'e-4 power technology has produced seven inventions represented by the composite transition joint restrictor (patent number ZL201410588156.6) and three papers represented by "Research on the Formation Mechanism of Negative Pressure in Propellant Pipelines". The successfully developed various component products and various innovative technologies can be promoted and applied to other spacecraft, shortening the development cycle, saving development costs, and having significant social and economic benefits.