Abstract: Aiming at the problems of frequent leakage and short service life of the mechanical seal in the power separator of polypropylene plant, this paper found that the high operating temperature of the sealing oil is the main reason for the short service life of the mechanical seal through analysis and calculation of the seal failure factors. The sealing oil circulation system was optimized by increasing the heat exchange area of the sealing oil heat exchanger and reducing the clearance of the screw sleeve of the pump. After one year of operation, the inlet sealing oil temperature of the sealing chamber of the power separator remained at 35 to 40 degrees and the leakage amount of sealing oil was basically stable at 0.3L per day. This optimization and transformation solved the problems of frequent leakage of mechanical seal of power separator, lengthened the service life of mechanical seal, reduced the number of shutdown times of the device, avoided the environmental pollution caused by plenty of seal oil leakage, and also created certain economic benefits for polypropylene plant.