In view of the frequent speed fluctuation problem of a single compressor unit under the parallel operation mode of two cracking gas compressor units, the components such as electro-hydraulic converter, self-excited valve, speed probe, pilot valve, and valve disc and valve seat of main stop valve were checked respectively during two rounds of shutdown inspection, and no abnormality was found. Based on the characteristics of the influence of ambient temperature on speed fluctuation and the different characteristics of three or four sections of fluctuation curve, it was found that liquid was accumulated in the overhead return pipeline of gasoline stripper, and the speed fluctuation problem was eliminated by adding thermal insulation and heat tracing.