Abstract: The effect of self-generated magnetic field of electron beams produced by laser irradiating on metal wires on the divergence of the electron beams is studied. The theoretical analysis and magnitude order estimation show that, between the laser spot and the right end of the wire, the electrons are subject to both electrostatic and self-generated magnetic fields, which leads to considerable collimation, and during their motion from the right end of the wire to IP stacks, the space-charge field and magnetic field roughly cancel each other and the divergence is maintained roughly. The classic trajectory Monte Carlo method is used to simulate this process, and the simulation result indicates that both the electron beam divergence and its dependence on wire length could be explained by the self-generated magnetic field.