Abstract: In order to decrease the radiation dose during the on-service maintenance of AP1000 canned reactor coolant pump, the auto-welding technology of the Canopy seal ring was studied under the same actual working process, and the remotely controlled weld equipment was developed and tested on the mock-up.The results show that under the optimal parameters, the backing weld of the Canopy seal ring is good, there is no lack of fusion in interlayer positon of the multi-layer and multi-pass weld, and the arc-starting and arc-ending positions are good.The auto-welding system has compact structure, and it is capable of stable welding on mock-up with good performance, and it can meet the auto-welding requirement during on-service maintenance of canned reactor coolant pump.