The influence of the total number of Si particles on the spatial density distribution of the particles (Si and He) and the velocity distribution of the Si-particles is investigated with Monte Carlo simulation. The results indicate that the maximum distance of high density peak from the target and the width of velocity distribution increase,and the time of reaching the maximum distance from the target firstly increases and then decreases with the increase of number of Si-particles. The splitting of the velocity is observed at the vicinity of 1.01×10¹⁵ and 1.01×10¹⁶ Si-particles.