Aiming at the problems of large amount of detection data of cable leakage fixtures and low manual detection efficiency in tunnel, a cable leakage fixture detection algorithm in tunnel based on the improved single shot MultiBox detector (SSD) algorithm is proposed. This algorithm uses feature maps with different scales to detect fixture objects, and improves the SSD network structure in terms of network width and network depth. The network width is deepened by combining the Inception structure, the residual structure is used to optimize network depth structure while increasing network depth, the depthwise separable convolution and 1×1 convolution structure are used to reduce the amount of model parameters and improve the model structure, so as to improve the model detection efficiency. The improved model is applied to the image detection of cable leakage fixture in tunnel. Experimental results show that the average detection accuracy of this algorithm reaches 86.6%, and the detection speed reaches 26.6 frame/s, which has obvious advantages over the original SSD algorithm and MobileNet SSD algorithm.