To solve the problem of selecting shape and size of the pinhole in the full-field X-ray fluorescence (XRF) imaging, the Geant4 Monte Carlo simulation software was used to simulate pinholes of 6 different types and 4 different diameters. The effects of the parameters on the spatial resolution which referred to the point spread function and the modulation transfer function were analyzed. The imaging process of different energy fluorescence X-ray plane sources is simulated, and the performance of image processing was analyzed by mean filter and the Richardson iteration method. The simulation results show that the pinhole model of the double conical-hole combined with the straight-hole has better sharpness and isoplanatism of the point spread function, a higher cut-off frequency of modulation transmission function, and better spatial resolution for X-ray of the energy less than 20 keV, which meant it is more suitable for full-field XRF imaging; the algorithm of mean filtering combined with the Richardson iteration performs better in full-field XRF image processing.