Abstract: It is a great challenge to control the welding deformation of aluminum alloy sheet because of its characteristics of both material and structure. This kind of deformation is a key problem of welding quality in the railway industry. In this paper, more attentions have paid to welding distortion of joints made of aluminum alloy sheet by MIG welding. Herein,numerical simulation was served as an effective tool for simulating welding deformation. Based on moving heat source model and sectional temperature function,the welding process of top slab of end wall with 2.2 mm thickness was simulated. Results showed that range of error between the deformation values of simulation and actual measurement was within 20%,the morphology of the welding pool simulated was basically in agreement with the experimentally measured results. Backward deformation and simulated structure coincide well with the results of actual welding process,welding process optimization of top slab of end wall was carried out by controlling arm pressure and position,welding sequence and backward deformation method.