Abstract: ［Objective］ Welding deformation in aluminum alloy carbodies remains a significant issue in the manufacturing process of city railway EMU. Conventional methods for predicting and controlling deformation often rely on past experience and actual vehicle trial-and-error, which have shown limited effectiveness. Therefore, it is necessary to use numerical simulation methods to predict the welding deformation trends of aluminum alloy carbody sidewalls of city railway EMU. ［Method］ The experimental materials are briefly introduced, followed by an explanation of the numerical simulation method for calculating sidewall welding deformation based on thermal elastoplastic theory and ABAQUS finite element analysis software. A real vehicle sidewall welding test is conducted simultaneously under conditions ensuring the same tooling distribution, pressure load, and boundary conditions as in the calculation. The simulated and measured deformation amounts of the sidewall are compared for the inverted welding and upright welding stages respectively. Four counter-deformation values (8 mm, 10 mm, 12 mm, 15 mm) are selected, and the maximum simulated and measured deformations of the vehicle sidewall after upright welding are compared under different counter-deformation values. ［Result & Conclusion］ The simulation calculation results are found to be numerically close to the actual measurements, with deviation between the two less than 30%. The maximum simulated deformation of carbody sidewall after inverted welding is 16.31 mm, while the maximum measured deformation is 17.00 mm. After upright welding, the maximum simulated deformation is 4.10 mm, and the maximum measured deformation is 5.50 mm. The optimal counter-deformation value for carbody sidewall is 12 mm, resulting in the minimal welding deformation of carbody sidewall.