A particle model that is based on Monte Carlo particle simulation arithmetic is built up to investigate the multipactor behavior on the surface of cylinder window disk in pill-box window. The regime of multipactor in the inhomogeneous electric field is obtained. The simulation results prove that the interaction between secondary electrons and window disk is sustained by magnetic field force on the upstream side. The multipactor phenomenon acts intensively in the area with a great electric field. The ponderomotive force does not devote any effort to multipactor on the upstream side. On the downstream side, the multipactor cannot be excited without strong enough surface electrostatic field because of the positive magnetic field force. With the increase of transmitting power, secondary electrons can obtain more energies. Due to the effect of ponderomotive force, the multipactor region transfers from the area with powerful electric field to the weak one on the downstream side. Besides, the resistance effect of electrostatic isolation on multipactor is also confirmed in the input port of cylinder waveguide.