The invention discloses an operating method for a welding fixture of a tricycle frame body. In the production process, a frame body oil cylinder, an oil pressure power machine and telescopic frame body oil cylinders are connected with an oil pump separately through oil pressure pipelines, and clamping air cylinders and air cylinder clamping angle clamp devices are connected with an air pump separately through pipelines; after welding fixture support frames lift and fall, the vertical spacing between fixture bottom frames and welding fixture main frame bodies is larger than the radius of the tricycle frame body of the preselected model; the clamping air cylinders and the air cylinder clamping angle clamp devices control clamping and locating for a welded frame body part separately through agas circuit control device; a locating turnover gear drives a welding tool platform face to turn over. By means of the operating method, through the welding fixture support frames, fixture turnover shafts and telescopic frame bodies are supported, an operator can conduct all-directional welding on the tricycle frame body part on the same tricycle frame body welding fixture and at the same station; in the welding process, the tricycle frame body is not deformed, the product quality and production efficiency are improved, and the product standard and safety are ensured.