The noise has a significant effect on the Signal to Ratio(SNR) of the trace gas absorption spectrometer, which is a standard for evaluating the imaging quality and trace gas retrieving capability. To quantitatively assess factors affecting SNR, and remove the noise of the spectrometer system, the noise source of the spectrometer is analyzed and the corresponding noise model is given. On this basis, the SNR model of the spectrometer is established in this paper. In addition, the effects of incident light intensity, integration time and system gain on the SNR are studied. The relationship between the different operating modes and different parameters and SNR is verified by the calibration experiment data of the spectrometer. And the main system noise is proposed: the linear deviation is used to determine the system offset noise. Besides, the temperature correction factor is obtained by using the dark current temperature correlation on the ground to realize the load in-orbit dark current correction. In the linear range of the detector response PRNU noise is corrected by the two-point correction method. The results show that the DN value of UV1 channel electronic offset noise is 2 625, and UV2 is 2 763. The dark current noise is the main part when the CCD imaging surface temperature is higher than 0 ℃, The temperature decreases to -20 ℃ when the rest of the noise plays a leading role to verify the best cooling temperature of the CCD; SNR increases with the increasing incident light response and integration time, the system gain will not affect SNR; PRNU noise was significantly improved by correction, decreasing from 3.32% to 0.47%, improving the spectral quality of the spectrometer. The noise analysis and processing methods are conducive to trace gas retrieve of further spectral data.