Abstract: In this paper, the difference scheme of the Maxwell's equations and the equations of the rate are given by us,at the same time,the equations of the primary electrons are solved by the Particle-in-cell (pic-method) and the primary electric current are obtained. To regard the primary electric current as the source term of the equations of the rate,the secondary electric current again are abtained, the algebraical sum of those currents driving electromagnetic pulse. Lastly,under the conditio are the source for ns of the nuclear burst, internal electromagnetic pulse produced by the prempt gamma photons are obtained.