In remote sensing imaging, extinction ratio and detector noise are important parameters that determine the accuracy of polarization imaging of nanowire gratings. To strike a balance between the two parameters for system optimization, a mathematical model using the two parameters and polarization noise was established in this paper. The photoelectron number received by large pixels was used as a measure to quantify the relationship between detector noise and system polarization noise. The effect of the two parameters on polarization noise was compared via a simulation wherein the polarization state of incident light was changed. Then, a platform to test the accuracy of polarization imaging with adjustable extinction ratio and exposure time was built to verify the mathematical model and simulation results. The simulation results demonstrate that when the extinction ratio of the system is greater than 20, wherein increasing detector noise by increasing the number of photoelectrons received by large pixels makes a greater contribution to the polarization accuracy than increasing the extinction ratio.