Abstract: Objective The reference basis is provided for the welding process parameters of engine exhaust gas recirculation (EGR) valve by studying the welding process parameters of 304 stainless steel flat plate lap welding. Methods 304 stainless steel plate lap joint spot welding test is carried out by tungsten inert gas (TIG) welding. The microstructures and mechanical properties of different welding angles (15°～75°) under constant current 140 A and different pulse frequencies (5～25 Hz) under peak current 200 A and base current 80 A are studied. By using the numerical simulation software and Gaussian heat source model, the temperature field changes of constant current welding and pulse current welding are studied. Results The results show that, as the welding angle increases, the horizontal size and penetration depth of the macroscopic size of the soldered joint and the max tensile force decrease gradually, while the vertical size and the width of the weld leg first decrease and then increase. As the pulse frequency increasing, the width of the weld leg shrinks gradually while the weld penetration increases slightly. Conslusion Reasonable parameter selection is beneficial to control the size of the soldered joint. Through numerical simulation, the temperature of pulse current presents a zigzag rising trend, and the temperature change in each pulse period shows the characteristics of rapid heating and rapid cooling. Due to the heat conduction process, the temperature change of the backside of the soldered joint center of the two welding methods has a certain hysteresis compared with the soldered joint center.