According to the features of laser active imaging, a new edge detection algorithm combining fractional differential and Sobel operator is proposed. The image preprocessing is completed by constructing a denoising algorithm based on the combination of wavelet soft threshold denoising and non-local means filtering. The deficiency of traditional Sobel operator is analyzed. Then the Sobel edge detection operator is improved by fractional differential, and a four-direction edge detection model based on the fractional differential and Sobel operator is proposed to complete image gradient operation. The maximum interclass differential method is used to automatically select the threshold, so as to achieve the binarization to complete edge detection. Experimental results show that compared with the traditional edge detection algorithms, the proposed algorithm can detect more image edge details and has better matching parameters.