Abstract: In view of the problems of fuzzy logic relation between the elements of the system, the polymorphism of fault mode, and the difficulty in obtaining the fault probability as a result of the complication of the hydraulic power system for coal mine tunnel drilling rig, a fault diagnosis method of hydraulic power system for coal mine tunnel drilling rig based on Takagi-Sugeno (T-S) fuzzy tree was proposed to overcome the limitations of traditional fault tree in fault diagnosis and analysis of the complex electromechanical hydraulic equipment. The method could timely and accurately obtain the fault information of equipment, and to find out the reasons and to take appropriate measures. Herein, research was conducted based on the hydraulic power system of ZDY25000LK drilling rig, with the hierarchical structure of the system analyzed and the performance variation described by the T-S fuzzy fault tree for analysis and tree establishment. Moreover, the fuzzy probability of the bottom events evaluated by experts was corrected according to the measurement method for centroid distance similarity, and thereby the trapezoidal fuzzy number of the probability of top event occurring in different fault conditions was solved. Furthermore, the importance of the bottom events were ranked based on the importance analysis of T-S probability, with the weak link of hydraulic power system in different fault conditions pointed out. The results show that the probability of serious faults is increasing for the events from component level to system level, and serious faults are more possible to occur if minor faults occur in multiple components of the system. As the fault degree of each event has different contribution to the occurrence of superior events, the fault should be located according to the importance ranking, and further the causes of fault could be judged. When the hydraulic power system has a serious fault, the working condition of safety valve, the internal wear condition of the oil pump and the internal oil running condition should be investigated first according to the importance analysis results. Therefore, the weak link of the system could be located rapidly with this method in various degrees of fault, which was verified in the engineering test of Tangjiahui Coal Mine of Huaihe Energy in Ordos, thus providing a reference basis for improving the reliability of coal mine tunnel drilling rig.