Abstract: Based on the beam coherence-polarization matrix and Collins formula,the on-axis polarization property ofGaussian-Schell model beam diffracted through an aperture was studied numerically.Simulation results showed that,due todiffraction effect,the polarization distribution of Gaussian-Schell model beam became non-uniform,there was oscillation of the on-axial polarization distribution,and that with increasing of the truncation parameter and decreasing of the spatial coherenceparameters and the transmission distance,oscillations strengthened gradually.While when the beams transmit on axis in freespace,polarization distribution in the near field is uniform,with increasing of the transmission distance and decreasing of thespatial coherence parameters,the on-axial polarization distribution increased.Thus the on-axial polarization distribution can becontrolled by apertures,which is useful for the application of partially coherent light.