Abstract: In view of low contrast ratio and view effect of monitoring images in coal mine underground, a single scale Retinex algorithm based on guided filtering was proposed for image enhancement of coal mine underground. The guided filtering, which can protect edge and make image smooth, is used for illumination estimation and convolution operation with original images, so as to get reflection component which reflects properties of the original images. For reflection component by anti-logarithm transformation, an improved local contrast enhancement method is used to improve contrast ratio of dark parts in the reflection image processed by antilogarithm operation, so as to get enhanced image finally. The experimental results show that the algorithm has better effect in promoting contrast ratio, enhancing details and denoising.