The invention discloses an assembly welding method for a marine riser and an auxiliary pipe bracket. The assembly welding method utilizes an assembly welding tooling and the assembly welding method comprises the following steps: step 1: a full circle barrel body, called a bracket annular plate, is shaped according to specifications of two semicircles corresponding to two semicircle brackets to be processed; the bracket annular plate, each pipeline fixing seat and corresponding bracket semi-rings are processed respectively; step 2: firstly, each pipeline fixing seat is firmly plugged into each corresponding auxiliary pipe bracket on the assembly welding tooling through pin shafts respectively; the bracket annular plate is placed between an adjusting jackscrew in the inner ring and each auxiliary pipe bracket in the outer ring; then, each pipeline fixing seat is assembled and welded with the bracket annular plate; step 3: each bracket semi ring is correspondingly welded on each pipeline fixing seat; step 4: crossing processing is performed, wherein the segmentation center line serves as the criterion to segment the bracket annular plate into two semicircle brackets; step 5: a hinge ear plate and a bolt connection plate are assembled and welded at the joint of the two semicircular brackets, and the marine riser and the auxiliary pipe bracket are obtained. According to the invention, mass processing is achieved and the precision is ensured.