Abstract: Based on the sub-model technology, the key welding joints between the lower cover plate and the vertical plate of a stainless steel metro car traction beam are studied, BS standard (British Standard) and ASME (American Society of Mechanical Engineers) standard are used to evaluate the welds. Through evaluation and analysis, it is made clear that the selection of appropriate welding joint and welding grade is an important part in BS standard evaluation; and the accurate definition of welding details is an important part in ASME standard evaluation. Considering comprehensively, the workload of BS standard evaluation is relatively small, therefore is suitable for the evaluation of vehicle welds; while the workload of welding joint definition in ASME standard is huge, but has relatively higher accuracy because it can avoid the random errors of artificial selection of welding joint and grade, therefore is suitable for the research of key welds.