Abstract: The sorting reliability of the gangue sorting robot is closely related to coal quality and sorting efficiency. It is necessary to study the sorting reliability of the sorting robot system. The existing reliability research of robot system mainly focuses on the structural reliability. There is no research on the task reliability of robot system, namely sorting reliability. In order to solve this problem, taking the cable-driven gangue sorting robot system as the research object, the sorting reliability is studied by fault tree analysis. Firstly, based on the structure of the gangue sorting robot system, the reasons for the sorting failure of the gangue sorting robot system are analyzed. The deductive method is used to construct the sorting fault tree of the gangue sorting robot system. Secondly, the occurrence probability of the bottom event of the fault tree is considered as an interval variable. The probability interval parameter of the top event of the sorting fault tree is obtained according to the interval property, the algorithm and the probability expression of the top event. According to the design requirements, the non-probabilistic reliability index which reflects the sorting reliability of the gangue sorting robot system is calculated. Finally, based on the formula of the non-probabilistic reliability index and the definition of fuzzy importance, an interval importance index is proposed. The interval importance of the events at the bottom of the sorting fault tree is solved and ranked. The results show that the sorting reliability can meet the requirements of sorting reliability of the gangue sorting robot. The increase of instantaneous gangue content in coal gangue flow and the failure of the industrial camera are important factors affecting the sorting reliability. According to the calculation result of the non-probability reliability index and the ranking of interval importance, the weak link of the gangue sorting robot system is found. Three improvement measures are proposed for the weak link. It is suggested to shake and mix the coal gangue flow before sorting. According to the identified gangue information, it is suggested to intelligently control the belt speed of the belt conveyor. It is suggested to add spare industrial camera in the gangue sorting robot system.