The transient method was used to simulate the argon arc welding process of large-scale thin-walled parts with multiple welds of TC4 alloy as aeroengine based on the SYSWELD professional welding simulation software. The influence of the welding line energy, fixture constraint state, and welding sequence on welding temperature field, welding deformation, and residual stress was analyzed. Results show that the welding deformation is increased exponentially with increasing the line energy, and the optimal line energy for argon arc welding is 310 J/mm. The application of welding fixture constraint can effectively reduce the welding deformation, but causes in the larger welding residual stress and wider distribution area. The decentralized symmetric welding can reduce the overall welding deformation of parts with multiple welds.