Abstract: A 3-dimensional numerical simulation code for microwave FEL in which space-charge force have been in eluded approxi matelv is worked out. The code constitutes of the electrons' energies and pandermotive phases according to the averaged single-particle equations derived by KMR, and the fields according to the paraxial wave equation. The particle motion is fully three-dimensional. The field solver is accurately three-dimensional for microwave simulation. The simulated results show that longitudinal space-charge force reduce the gain and saturation power about 15%,and increase the synchrotron period of the electrons.