Abstract: In order to evaluate the reliability of the space flexible actuator in orbit，the reliability verification test method of the actuator was given according to the characteristics of complex in-orbit operating conditions，small sample size and long life.Firstly，on the basis of analyzing the structure composition and working principle of the actuator，the reliability characteristic quantity of the actuator was determined.Then，taking the life-type reliability test as the basic idea，aiming at the main failure mode of on-orbit fatigue fracture failure of flexible components，the fatigue test load spectrum design was proposed according to the load data of typical onorbit operating conditions，the accelerated fatigue life test of the flexible component was carried out using the load spectrum，and the reliability evaluation results of the actuator were given based on the fatigue life test results.Finally，taking a certain type of space flexible actuator as an example，the reliability test was carried out based on the accelerated fatigue test of the flexible component，and the reliability evaluation results of the actuator were obtained.The research results show that the reliability of the actuator meets the requirements of the index，and that the evaluation results conform to the engineering practice.The proposed reliability verification test method can provide an effective technical approach for the quantitative reliability evaluation of the space flexible actuator，and can provide a reference for the reliability verification of the spacecraft motion mechanism.

Key words: actuator, flexible components, load spectrum, accelerated fatigue test, reliability assessment