This paper introduces the process flow and functions of compression unit in ethylene plants, as well as the principles and harms of quench water emulsification. The correlation mechanism between the operation process fluctuations and operation condition changes of compression unit and the quench water emulsification is analyzed in detail. In order to reduce the adverse effect of compression unit on quench water emulsification and ensure the stable and efficient operation of ethylene plant, some measures are proposed to optimize the operation of compression unit and strengthen the process control.