Vignetting effect during infrared imaging is the phenomenon that image plane center region is bright but edge is dark. The vignetting effect is very serious, so it is necessary to correct the vignetting effect when the system is used. First, the cause of the vignetting effect was analyzed. Then, a fast correction method was proposed. The background information was extracted, and the background gray distribution was obtained by polynomial approximation. To evaluate the correction effect, the concept of variance between rows which has statistical significance was put forward. To verify the correction method, two kinds of scenes were used. Variance between rows was reduced to 13.6% and 3.8% compared with uncorrected images. The effect of the correction method is ideal.