Sub-wavelength periodic grating has special characteristics that are lacking in traditional grating. In this study, a flexible double-layer metal grating polarizer is designed and fabricated using a strict coupled wave method. Through nanoimprinting technology, sub-wavelength grating with a period of 278 nm, depth of 110 nm, and duty cycle of 0.5 is prepared on a square polycarbonate (PC). A 70 nm metal aluminum layer is deposited on the fabricated dielectric grating by magnetron sputtering, and a double-layer metal structure is fabricated. A flexible double-layer metal grating polarizer is developed, and the performance of the polarizer is tested using a spectrum measurement system. Experimental results showed that when the wavelength range of the incident light was 350-800 nm, the flexible double-layer grating polarizer had good polarization characteristics. The polarized light transmission efficiency and extinction ratio were as high as high as 48% and 100000, respectively. The manufacturing process involves only nanoimprinting and metal evaporation processes and thus excludes coating, stripping, and etching of the imprint adhesive. Therefore, our method exhibits evident advantages in terms of low-cost and batch production of large-area polarizers and thus can be widely used in the manufacturing process of semiconductor optoelectronic devices such as optical-detection and optoelectronic devices.