A numerical analysis method was proposed to predict the welding residual stress in 2.25Cr-1Mo steel pipe considering solid-state phase transformations. A thermal elastic plastic finite element (FE) model considering effects of martensite transformation was developed based on commercial ABAQUS software. Continuous cooling transformation (CCT) diagrams were employed to simulate the fraction of martensite in fusion zone, coarsegrained heat affected zone and fine-grained heat affected zone. The Koistinen-Marburger relationship was used to trace the formation of martensite. The effects of both volume change and yield strength change due to phase transformation on welding residual stress were considered using the proposed FE model. The result shows that the phase transformation has significant effects on the welding residual stress in multi-pass butt weld of pipe. The predicted simulation results by the proposed numerical method are generally in good agreement with experimental results.