By analyzing the formation mechanism of a supersonic gas jet,a set of equations which describe the atomic beam properties were established.The influence of initial temperature,initial pressure,background gas pressure and pumping speed was discussed in detail.A simulation program was developed based on the equations,and the results under different initial conditions were obtained.The results are in good agreement with the experimental data,and suggest that,in order to get much smaller transverse momentum in collision experiments,it is necessary to lower the initial temperature and the initial pressure of the supersonic gas jet,together with increasing the pumping speed.These results are very instructive for construction of a new generation of cold supersonic gas jets.