Aiming at the problem of redundancy in the phase space reconstruction of sample entropy algorithm, the phase space reconstruction process of sample entropy algorithm was replaced by a symbolic variable matrix, and an improved sample entropy algorithm was 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 are highly consistent with the sample entropy algorithm, and the computational efficiency of the algorithm is much higher than that of the sample entropy algorithm.