This study focuses on the experimental and numerical investigations for the degradation characteristics of a metasurface polarizer. The metasurface has a stacked complementary structure that exhibits a high extinction ratio of the order of 10,000 in the near-infrared region. However, its performance has significantly degraded over time. To clarify the origin of this degradation, the effects of surface roughness and metallic loss are investigated numerically. The degradation is mainly attributed to increase in the loss. These numerical calculations also reveal that the extinction ratio is enhanced by adjusting the thicknesses of the complementary structures to different values. This study paves a way to realize a metasurface polarizer that has a low sensitivity to the time degradation and has a high extinction ratio.