The invention provides a centralized processing method for opening and welding a plastic oil tank, comprising the following steps: the oil tank is arranged on the clamp of a worktable, positioned and fixed, the worktable is moved to the workpiece position of a processing center, the oil tank is opened and welded by the processing center on the workpiece position, the worktable is moved out of theprocessing workpiece position, and the oil tank is taken down. The invention has the advantages that the traditional production line is substituted by the processing center, thus decreasing the spaceoccupied by equipment, increasing the production efficiency, and ensuring the processing accuracy and improving the production quality as the oil tank is opened and welded on the same workpiece position and the oil tank is not moved.