Rigorous coupled wave analysis (RCWA) was used to investigate the polarization characteristics of subwavelength aluminum wire grating in near infrared. Upon exposure to the atmosphere, a layer of Al2O3 forms rapidly on the aluminum wires, so the effect of metal oxide layers on the polarization properties is modeled and analyzed. It is shown that subwavelength aluminum wire grating with oxide layers forming on the wires still offers excellent polarization properties. As the thickness of the oxide layer increases, the transmission coefficient increases, but the extinction ratio decreases. In addition, a magnesium fluoride (MgF2) layer was proposed to deposit between the aluminum wires and the substrate to enhance transmission coefficient. The theoretical research shows that subwavelength aluminum grid grating has high transmission coefficient and extinction ratio in near infrared, as well as uniform performance with wide variations in the angle of incidence. These features with their small size make it desirable for use in optical communication and allow more compact component designs.