Abstract: An algorithm of key frame extraction is proposed by using the inter-frame correlation, which is used to extract key frames for road monitoring video photographed by fixed cameras. Firstly, the pre-processing is utilized to operate frames, and then the color frames change to gray frames. Secondly, the sliding window is combined with the gray frames to determine key frames through comparing the threshold with the relative deviation of the inter-frame correlation and autocorrelation. The experimental results show that the process of the algorithm is clear, and the key frame consistent with the visual can be extracted effectively and the level of sensitivity adjusts to the threshold well.