The invention relates to a visual detecting method based on decoupling detection for circular seams. The method is used for detecting, recognizing and welding the welding seams of circular welding pieces with V-shaped grooves. The method is characterized by comprising the following steps: first, processing pictures and extracting features; and second, decoupling image information. For the method, according to the three-dimensional welding seam feature information extracted by decoupling single frame images, the deviation value of a welding gun in a two-dimensional plane relative to the welding seam center can be calculated, the accurate positioning of welding spots in three-dimensional space can be realized, the decoupling algorithm is performed by monocular vision when the two-dimensional welding seam information is obtained, the tedious matrix transformation when the welding seam information is demarcated is avoided, the demarcating and calculating time is greatly saved, and the real-time performance of a system is obviously improved. On one hand, building a complex imaging model of a camera is avoided, and on the other hand, the demarcating precision, the robustness and the applicability of the camera are improved.