Abstract: To solve the problem of reliability of actuator group system for FAST, the concepts of the group system and the reliability of group system is defined. And the mathematical model of the reliability for group system is built based on the weighted value theory. The engineering significance of the weighted value of actuator is expounded. The computational method of the weighted value and availability of actuator is proposed. The reliability of actuator group system of FAST from March to August 2019 is calculated quantitatively, and calculation result is 0.997 85. According to the reliability model of group system, the reliability growth method of group system can be got：increased the mean time between failures(MTBF) of the subsystem and reduced the mean time to repair(MTTR)of the subsystem. The solution of reliability growth of actuator group system for FAST is designed. To increase the MTBF of actuator, the optimal cost-performance reliability growth scheme is planned： the part reliability growth can be designed and tested before the whole reliability growth design and test. To reduce the MTTR of actuator, the intelligent fault diagnosis and prediction system that base on technology of PHM is proposed, so that the maintenance mode of FAST actuator changed from passive to active. Both the problem of reliability and reliability growth of actuator group system of FAST are solved by the theory of the reliability of group system. Meanwhile, it can be used as the reference for similar research of reliability of group system.

Key words: actuators of FAST, group system, reliability of group system, the weighted value, reliability growth of group system, status maintenance