Abstract: The welding deformation of high-speed rail roof has been a problem to be solved in engineering, the numerical simulation on the welding process of roof can predict the welding deformation quickly and effectively, and therefore it can provide the basis for improving the welding process. However, the rail roof is very huge and has numbers of welding lines, it is difficult to predict the deformation accurately and efficiently by using the present simulation method. Based on the intrinsic strain theory, the welding deformation of roof was quickly and accurately obtained by improving the existing calculation model according to the MIG welding process of aluminum alloy. The results show that when the high-speed train roof welds are welded with different sequences, the deformation trend is almost same but the deformation degree is quite different. And the roof has the minimum deformation when welding in the order from outer arc surface to inner arc surface and from center to two sides for the same arc surface.