electromagnetic field under non relativity is carried out，and the charge’s motion is decomposed into: 1) uniformlyaccelerated linear motion along the direction of magnetic field; 2) uniform linear motion perpendicular to the direction of electric and magnetic field; 3) circular motion with uniform rate perpendicular to the direction of magneticfield. Therefore the complete kinematics equations of electric charge are deduced. Then，the kinematics equations are reduced and simplified，and the projection trajectories of charge in the xy plane under different initial velocities are made and analyzed，of which characteristics and internal reasons are pointed out. An example is given to illustrate the space trajectory of electric charge，and the commonness of it is pointed out. Three special cases of uniform orthogonal electromagnetic field are discussed. In addition，it is pointed out at the end of the paper that the core idea of the method in this paper is the switching of reference frame.