Abstract: We think that scattering of particles of the magnetotail in forming of precipitating particles is very importment.In this paper,the pitch angle changing of charged particles of the magnetotail under the action of the dawn-dusk electric field is studied by evaluating about 900 trajectories by computer.The results show clearly that the charg-ed particles of the magnetotail under the action of the dawn-dusk electric field undergo evident scattering process.The particles of the magnetotail which move through the nonperturbation region are reflected many times inside the nonperturbation region,the magnetic moment is no longer invariant,and when they leave the nonperturbation region,their pitch angles are changeable.This change makes isotropic initial pitch angles distribution change into a Maxwellian state,when the particles are away from the neutral line and enter into the region of near earth.The space career of these particles are also studied,and it is found that they undergo space separation (dawn-dusk separation,latitude separation and a relative separation between the protons and electrons) when they leave the magnetotail and enter into near earth with the clear precipiting pattern of the particles.