Abstract: In order to liquefy natural gas using differential pressure of gas-distribution station pressure, the natural gas liquefaction process with RC before the expander is used commonly. The precooling process has important influence on the whole process unit's energy consumption. Aiming at this problem, the structure of the precooling process is optimized. Based on the method of simultaneous module, mathematical models of different compression section number is established, and the simulation calculation is carried on. Finally the optimal compression section number three is gotten, so it is utmost likely to reduce the energy consumption of the device and improve the economic benefit.