It studies the optimization of charged particle optical system and proposes to separate the optimization of aberration from the optimzation of field in lens. In the optimization of aberration, the implication constraints are considered. In this optimization, it needs to do some simple integral calculations so that the calculation of field which will takes a lot of time is avoided. In the optimization of filed in lens, the mathmatical model is just the same as in other electromagnetic system. Therefore, the optimzation methods of electromagnetic system can be used to optimize the field in lens. In the end, two examples for optimization are given to verify the new method.

In electron beam lithography system,focus ion beam system and cathode ray tubes,the space charge effect caused by the interaction of every particle affects the quality of the device.A lot of scholars have already studied the space charge effect.As so far,Monte Carlo method is often used to calculate the space charge effect in the transportation of particles.This paper tries to use Monte Carlo method to calculate the space charge effect in the beam form region.The 'edge effect' is analysed and some new ways are proposed to decrease the'edge effect' in the simulation.