Global shutters have advantages in hyperspectral imaging, mapping, and star-sensing applications for Earth observation, but their application effects also depend on high signal-to-noise ratios. According to the characteristics of CMOS imaging, a low-voltage reference source circuit capable of sourcing and sinking current and a focal plane electron with low thermal distortion are designed. A method of receiving multi-channel serial data with uncertain initial state of power-on is proposed.According to the influence of the parasitic light sensitivity unique to the global shutter, the multi-point fitting correction method based on line-by-line counting and taking the middle line as the reference is adopted.The front-illuminated CMOS imaging system and cooled back-illuminated EMCCD are tested according to EMVA1288 standard.The standard deviation of the single image before and after calibration is 3.37 and 0.42 respectively, the maximum SNR is 123.37, and the maximum SNR of the EMCCD is 359.43. The results show that the correction method can effectively reduce the fixed pattern noise of the global shutter. There is a big gap between the SNR of the area array CMOS in the global shutter mode and that of EMCCD.