Using 3D MC code and PIC code, model of electromagnetic pulse (SGEMP) generated in the cavity system radiated by SG-facility is calculated. The simulated results show that the intensity of electric field could be 2.2 MV/m and magnetic field be 0.8×10^-3 T under irradiation of the bremsstrahlung X-ray point source with full width at half maximum 2.9 ns, average energy 10.3 keV produced by SG-facility irradiating the end of cylinder cavity. The electric field is mainly axial and the magnetic field is primarily azimuthal. Both electric field and magnetic field are concentrated near the emitting surface, with the pulsed DC field being predominant and the amplitude of the AC radiation field being relatively smaller, at the level of kV/m. The effect of fluence on SGEMP is also studied, showing that higher fluence leads to faster axial variation of the electric field and larger proportion of the AC radiation field.