The noise characteristics of a low light level imaging system based on the scientific complementary metal-oxide-semiconductor (sCMOS) image sensor are analyzed. The system noise model is established and the system noise is measured. The results show that the root mean square value of system noise is less than 1 e-. The signal-to-noise ratio (SNR) model is built, the calculated SNR of this low light level imaging system is superior to 1 under 10-3 lx night light conditions, and the error between the theoretical and measured results is less than 10%. An adaptive stripe noise processing method is proposed to effectively eliminate the row stripe noise of image under low light conditions and the contrast limited adaptive histogram equalization method is applied to improve the contrast of image with a high dynamic range.