The separation of methane in high pressure demethanation system is discussed in this paper. Based on the analysis of the trend of methane in demethanation system, the influence of the feed temperature of C₂ condensing fractionator on the refrigerant load of ethylene is discussed. By adding liquid phase methane from the – 140℃methane/hydrogen separation drum to the reflux drum of demethanizer, the ethylene loss and the refrigerant consumption of ethylene can be reduced. Finally, the comprehensive analysis of the feed temperature of C₂ condensing fractionator and the bypass line flow rate is carried out, and the local optimal solutions are obtained.