The invention relates to a process for processing a side wall of an aluminum alloy bodywork of a rail vehicle, which comprises the following steps: processing a single side wall board, namely carrying out mechanical processing except window cutting; assembling and welding the side wall board, namely assembling and welding all aluminum alloy profiles together, and polishing welding seams; integrally clamping the side wall, namely fixing the side wall on a workbench; measuring a side wall window, namely measuring the design size of the window and the processing size at a processing position, and inputting the measurement result to a numerical control processing center; integrally processing the side wall window, namely calling a numerical control processing program to process the window; and polishing the side wall window, and finally handing over a side wall finished product. By adopting the process flows of firstly assembling and welding all aluminum alloy profiles forming the side wall together and then cutting and processing the window, the process can effectively control the influence of welding deformation on the processing precision of the window, ensure the processing precision of the side wall, improve the appearance quality of the product, improve the production efficiency, reduce the labor intensity of workers, and reduce the production cost.