对于中和室内的脉冲气体，用蒙特卡罗方法模拟了气体压力沿轴向的分布。并用模拟进气系统和气压瞬时测量系统，对模拟结果进行了验证。得到与模拟结果较为一致的曲线，从而为注入器真空系统的设计提供了可靠的依据。并通过实验结果，给出了气体靶厚的建立时间约为６０ｍｓ。 For the pulsed gas in the neutralization chamber, the distribution of the gas pressure in the axial direction is simulated by Monte Carlo method. Simulated results were verified by simulating air intake system and air pressure transient measurement system. The curve which is more consistent with the simulation results is obtained, which provides a reliable basis for the design of injector vacuum system. Through the experimental results, the establishment time of gas target thickness is given as 60ms.