Nanowire-grid polarizer is of a periodic sub-wave structure of metallic nanowire on the substrate, fabricated by nanoimprint technology. Different from traditional polarization prism and dichroic polarizer, the nanowire-grid polarizer has many advantages such as compact size, easy integration and high polarization performance. However, in the ultraviolet and visible regions, it is infeasible to improve the performance of single layer nanowire structure by reducing the character size of nanowire because of the bottleneck of lithographic process. The double-layer nanowire-grid structure could improve the polarization characteristics at some special wavelengths but not full-wave band of ultraviolet and visible regions. In this paper, we propose a tunable double-layer structure to enhance the extinction ratio and transmission at each wavelength by tuning the distance between two nanowire-grid polarizers through adjusting the voltage applied to PZT. To calculate the transmittance and transmission extinction ratio of tunable structure, software VirtualLab is employed and the Fourier model method is used. The numerical simulation results show that the tunable structure have a higher polarization characteristic in ultraviolet and visible regions than single layer structure and double layers structure.