A numerical simulation of the electrical breakdown in dynamic mode of single crystals of ammonium perchlorate has been carried out. The system of differential equations was solved, which described the processes in the equivalent circuit of the pulse voltage generator together with the kinetic equation of impact electron multiplication and the heat balance equation. The dependences of the electric strength of ammonium perchlorate in dynamic mode on the interelectrode distance and the duration of the leading edge of a high voltage pulse were calculated. Obtained numerical simulation results are in good agreement with the known experimental data of electrical breakdown of ammonium perchlorate in the dynamic mode.