In order to restrain the effect of CMOS image sensor fixed pattern noise(FPN) caused by the gain mismatch of readout amplifier circuit, to improve the quality of imaging, a method of fixed pattern noise correction based on the dark current is proposed in this paper. Compared with the traditional correction methods, this method has simple correction system, and the algorithm is easy to be implemented. The images before and after correction were evaluated via the grayscale variance, and the evaluation results show that in the background image formed by dark current, the grayscale variance of after corrected image reduced by 4 orders of magnitude compared with that before correction. As for the CMOS image under uniform illumination condition, the grayscale variance of after corrected image increased by 2 orders of magnitude compared with that before correction. The evaluation results and related conclusions are useful for the future study of dark current background images and correlation correction methods.