The invention discloses a heavy type part hydraulic clamping and welding positioner, and belongs to the field of engineering machinery. The positioner comprises an L-shaped welding positioner main structure, a clamp body and a transmission mechanism. The clamp body comprises a positioning shaft, a pressing block, a positioning base, a clamp body base and a rotary hydraulic oil cylinder. The rotaryhydraulic oil cylinder is fixed to the clamp body base and fixedly connected with the pressing block. The positioning shaft and the positioning base are fixed to the clamp body base respectively, andthe clamp body base is fixed to the L-shaped welding positioner main structure. According to the heavy type part hydraulic clamping and welding positioner, it is ensured that clamping is rapid, efficient and accurate and saves labor in the large workpiece welding process, the product welding efficiency is improved, the transmission mechanism simultaneously achieves the transmission function and the rotation function, and the transmission mechanism has the double functions of load transferring and hydraulic fluid transferring.