In this paper, the magnetic field parametric switching method for controlling t he beam_halo chaos in the period_focusing channel(PFC) is studied. The law of t he parametrical switching control is presented . The simulation results demonstr ated that the chaotic envelo pe of the ion beam can be controlled well by this method. Then the method is app lied to the multi_particle model with the period_focusing magnetic field channel . The PFC simulation results show that beam halo_chaos for five different kinds of beams can be controlled well. The beam halos and its regeneration can be eliminated. This method is easy to realize in experiment.The research offers a valuable reference for the design of the PFCs in the high_current linea r proton accelerators.