Due to complexity, bigger size and multi-seams of the box welded structure of railway vehicles; it is difficult to predict welding deformation using traditional methods. The methodology of multi-pass prescribed thermal cycle and the local-global approach are introduced. And also the application of the methods proposed on the deformation of railway vehicle large welded structures are discussed based on SYSWELD and Pam-assembly simulation software. This paper finds not only solving engineering problems but also comparative economic forecasting and controlling welding distortion methods.