Abstract: The physical mechanism of field emission was analyzed. The launch conditions of field emission in three-dimensional Yee grid model were deduced and implemented, and the Pade grid algorithm was used to encrypt the cutting-edge grid. The current-voltage relationship and the 3/2 power of the space charge limited flow at high voltage were obtained for a wedge-shaped cathode field emission model, which verify the correctness of simulation. In order to deal with the great amount of computation due to large particle number and huge grid, the message passing interface (MPI) was used, and a more than 3.0 parallel speedup was obtained.