The weldability of Q345R steel and 20 steel is analyzed, welding procedure TIG+MAG is formulated, the optimum welding specification parameters are determined, welding procedure test and qualification are carried out, the surface and internal quality of weld are verified by penetration testing and radiographic testing, and the properties of welded joints are verified by mechanical properties tests. Combined with the welding structure of high pressure electrode boiler body and branch pipe,the experimental results are applied to the welding of high pressure electrode boiler body and branch pipe. Ultrasonic testing and penetrant testing are performed on the welds according to the requirements of NB/T 47013.2 and NB/T 47013.5, the test results meet the grade Ⅰ quality requirements of the corresponding standards, and good welding results are obtained.