Aiming at the problem of redundancy in the phase space reconstruction of sample entropy algorithm, the phase space reconstruction process of sample entropy algorithm is replaced by a symbolic variable matrix, and an improved sample entropy algorithm is established. The analysis of white noise and powder noise simulation signals shows that the improved sample entropy algorithm can extract signal features effectively and has high computational efficiency. In the past, bearing clearance faults of complex compressors were studied, and the improved sample entropy algorithm was applied to extract features and compared with sample entropy. The feature extraction results of the method were highly consistent with the sample entropy algorithm, and the computational efficiency of the algorithm was much higher than that of the sample entropy algorithm.