The large-field visual landing guidance system needs to quickly detect the cooperative targets mounted on the UAV during the autonomous landing of the UAV. The cooperative target exists in the form of light spots on the image, so in order to meet the real-time requirements of the system, a fast spot detection algorithm based on contour features is proposed in this paper. Firstly, according to the characteristics of light spots in the image, the target clipping method is used to extract the light spots in the original image, so as to reduce the amount of computation. Then, through the image preprocessing, the irrelevant information and noise interference in the background are eliminated to enhance the clarity of the spot. Finally, the least square algorithm is used to locate the center of the light spot by ellipse fitting. The experimental algorithm is compared with other spot detection algorithms so as to verify the real-time performance of the system. The results show that the proposed algorithm can reduce the running time to 36ms while ensuring the accuracy.