In view of the objetive limitation of sample data acquisition during the debugging process of secondary equipment in substations. It is difficult to analyze and judge the reliability of the system based on small-size sample data. This paper studies the reliability analysis method of secondary equipment based on Bootstrap method for sample expansion. Firstly

parameter distribution estimation based on Bootstrap method is discussed. Then

a Bootstrap sample expansion method that combines empirical information and sample structure transformation is proposed to overcome the problem of concentrated sample data and limited information coverage in classic Bootstrap method. On the basis of parameter distribution estimation

the reliability of secondary equipment is analyzed based on the probability distribution of the operating threshold. Finally

the effectiveness of the proposed method is verified through simulation experiments.