Abstract: The study uses the particle-in-cell method to simulate the focusing of intense electron beam with the thin magnetic lens. The focusing model of intense electron beam was established and to simulate one experiment on Dragon-I accelerator. The simulation result is very close to the experimental one, which proves the validity of the model. The influences of some parameters of electron beam on focusing were simulated. In the simulations, the best envelope diameter of incident paralled beams is 20.0-22.5 mm. For the effects of beam emittance and energy spread, the simulation results agree well with theoretical ones. Moreover, the focal spot of small size can be obtained, only when the envelope diameter and the phase of incident beams are matched.