This article presents the research method to simulate the arc welding process for shipbuilding structural steel with a most comprehensive way. Not only simulation of the heat transfer process, deformation and stress in the welded joint, the authors also calculated and simulated the phase transformation process in welded joint. The author has developed a computer's program that runs on Sysweld software to calculate and simulate the complete behavior of shipbuilding structural steel in electric arc welding process, as the basis for ensuring the quality of welding fabrication.