The welding process of common fillet welds along three orthotropic directions in a large-scale metal structure is simulated by finite element method. Five different welding sequences are selected, and the effects of these welding sequences on the residual stress fields of T-joints are simulated and the optimal welding sequence is gained. The results show that the welding sequence affects not only the distribution of temperature field but also the amount and distribution of residual stress. The backstep welding method,which welds middle section first and then welds both ends, can effectively reduce the residual stress of T-joints.