This paper introduces the anomaly of gradual increase in axial displacement of cracking gas compressor, and provides a detailed analysis of the reasons for the change in axial force of rotor in the medium-pressure cylinder of centrifugal compressor through troubleshooting. By analyzing the causes, it comes to the conclusion that the gradual increase in the axial displacement of rotor in the medium-pressure cylinder is due to the scale formation of stator of the compressor. Through injecting wash oil with higher distillation range into the cylinder of the compressor to wash the flow passage, the scale formation problem of the stator of the compressor is solved, thereby changing the axial force distribution of the rotor and finally removing the risk of gradual increase in axial displacement that may cause equipment failure.