The geomagnetic cut-off rigidity can effectively measure the shielding effect of Earth's magnetic field on cosmic ray particles. In this paper, the single particle orbit theory is used to simulate the movement of cosmic ray protons in the Earth's magnetosphere and the specific location within the magnetic field along the vertical direction to the earth center. Based on the establishment of T04 and IGRF2000, the fourth-order Runge-Kutta method is used to simulate the trajectories of particles. The vertical cutoff rigidities of global cosmic protons around the height of 450km above Earth's surface at two moments in November 2004 are calculated. The value change of geomagnetic vertical cutoff rigidity with the magnetic latitude and magnetic longitude is analysed with the help of 684 calculation results at the same moment. The changes of protons vertical cutoff rigidity with the height from Earth's center, at the position of magnetic latitude of 30°, magnetic longitude of 0°, 45°, 90°, 135°, 180°, 225°, 270°, 315°, are also simulated. Simulation results show that the change of geomagnetic effective vertical cutoff rigidity with the increasing height from the Earth's center is getting more and more slow and slower along the sunny direction to the magnetic tail.