Abstract: The field distribution and ion trajectory,in the ion acceleration region comprising 4 pieces or 23 pieces of membrane hole electrostatic lens,were mathematically modeled,theoretically analyzed and numerically simulated with COMSOL software for design optimization of the miniaturized ion source.The influence of the key variables,including the number,position,spacing and voltage of the membrane hole-lens,on the energy and divergence of the ion-beam was investigated.The simulated results show that when it comes to precise ion-beam confinement,the 4 focusing lenses-set outperforms the 23 lenses-set. To be specific,when the 1^st lens is installed 12 mm from the 2^nd one(the spacing of the rest lens is 1 mm) and at an optimized lens voltage of 510 V,the ion-beam has the smallest divergence angle of 3° and the highest energy of 480 eV.