This article analyzes the problem of over high outlet pressure at the end section of compressor in the ternary refrigeration system of an ethylene plant. Combining with the trend of lighter feedstock, a new method for reducing the pressure of the ternary refrigeration compressor using LPG cold energy is proposed. The existing LPG raw material preheating system is replaced with the newly installed LPG cold energy reconditioning system. While preheating LPG raw material , this part of cold energy is recovered by the ternary refrigeration system to alleviate the problem of over high outlet pressure at the end section of compressor in ternary refrigeration system.