Abstract: Based on the beam coherence-polarization (BCP) matrix and the propagation law,the expressions for the degree of polarization and intensity distribution of nonuniformly polarized (NUP) beams through an aperture are derived. Numerical examples for a type of uniform intensity distribution NUP beams are given. It is shown that remarkable changes in both polarization and intensity distributions take place after the aperture. There are oscillations of the degree of polarization at the transversal plane and the intensity profile is nonuniform. However,the polarization becomes uniform in the far field.