In this paper, we calculate permanent magnet theoretically for a multicusp ion source Coulomb collision between electrons is treated with the "binary collision" model and collisions between the electrons and hydrogen species are treated with the "null-collision" method. A 3D PIC-MCC simulation algorithm is developed, and based on this algorithm the electron deposition process in multicusp ion source is simulated, and the multicusp magnetic field effects on the electron energy distribution and spatial distribution are analyzed. The results show that the spatial non-uniformity of electron distribution comes from high energy electron B× ▽B drift in the filter field.