Spot welding is increasingly used in industrial production. As the main carrier of spot welding, the welding tongs structure and welding stability are very important for welding quality. Three ARO servo guns have been analyzed by finite element. In order to to meet the 6.5 kN welding pressure requirement of new production line,structures of gun have been optimized based on simulation.At the same time,the mechanical installation mode is also optimized after simulated under production conditions with DELMIA software. The simulation results show that all the optimized guns can meet requirements of new production line.