To solve the problems of low contrast, strong noise and lack of detail information of the images taken in low illumination environment, a low illumination image enhancement method based on quad-stable stochastic resonance is proposed. The interaction of noise and nonlinearity can produce stochastic resonance. Based on the theory, a nonlinear quad-stable system is constructed and its Kramers escape rate is analyzed. In order to measure stochastic resonance effect of quad-stable system objectively, the variance is used as an index of image stochastic resonance. The approximate analytical expression of the system output image variance with respect to noise intensity is established, and the effect of noise on image contrast enhancement is discussed. The theoretical analysis and numerical simulation indicate that with the change of noise intensity, the quad-stable system output image variance shows a single peak characteristic, which means that the phenomenon of image stochastic resonance appears. Compared with the classical bistable system, the peak of the formant produced by the quad-stable system is larger and the resonance effect is stronger. The proposed method is compared with the histogram equalization algorithm, single-scale Retinex algorithm, multi-scale Retinex with color restoration algorithm and bistable stochastic resonance method by subjective evaluation and objective evaluation indexes. The experimental results show that the visuals of the image enhanced by quad-stable stochastic resonance is the best, which information entropy is 7.7, and the estimated noise variance is less than 0.002. Under the joint action of low illumination image and noise, the stochastic resonance effect produced by the quad-stable system is more intense. This is beneficial to improve the noise utilization rate and further improve the image quality, so that the quad-stable stochastic resonance method has more advantages in low-illuminance image enhancement.