In order to simplify the optimization and analysis of the large helium liquefaction cycle,genetic algorithm(GA) was adopted in characteristics optimization Collins helium liquefaction cycle with nitrogen pre-cooling,the global solution was searched given parameter to get the maximum liquefaction rate. GA is proved to be applicable for optimization of the cryogenic process. The relation curve of liguefaction rate and temperature difference in heat exchanger hot end was plotted,which shows a decreased liguefaction rate with increasing the temperature difference.