The goal of the study is to identify the effect of the grid geometry parameters on the performance of the ion optics design. The combination of particle-in-cell method and Monte-Carlo collision method is used to study the influence of the critical geometrical parameters on the beamlet current capability, beamlet divergence angle and capture of charge exchange (CEX) ions. Moreover, the variation trends of beam divergence angle and impingement CEX ion are also investigated under different specific impulse conditions. The results show that with the increase of the screen grid aperture radius, the beamlet current capability, beam divergence angle and saddle point potential are increased. An increase in the accelerator grid radius produces a decrease in impingement CEX ion current. The beamlet divergence angle and the impingement CEX ion current both increase with the incremental thickness of accelerator grid. When the specific impulse is 8000 s, the change of the acceleration stage gap has little effect on the beamlet current capability. In addition, the higher the specific impulse, the smaller the beam divergence angle and the fewer the impingement CEX ions.