The Low Energy Consumption Technology (LECT) developed by SEI is studied in detail, the influence of condensating-fractionating tower design on demethanizer system is analyzed, and the demethanizer system is simulated and optimized. The results show that properly reducing the temperature of condensating-fractionating tower can greatly reduce the ethylene loss while improving the purity of hydrogen product. Maintaining the overhead temperature of condensating-fractionating tower at about -122 °C can ensure relatively high ethylene yield and hydrogen purity and keep the consumption of cooling capacity within a reasonable range.