Traction devices are power transmission components of railbound vehicle. This article discusses the gearbox mechanical properties numerical calculation and strength analysis. It established calculation model based on field test parameters. And it finished analysis about elastic deformation of large displacement and contact problem of nonlinear finite element method during numerical calculation. With comparison of energy strength theory and ASME VIII-2 standard, it chooses the suitable strength method for gearbox. With definition of key parameters, the mechanical properties numerical calculation results were given in different load conditions. According to displacement, strain and stress analysis, the gearbox strength is analyzed based on ASME VIII-2 standard. The results show: under field test loads, the gearbox satisfies strength requirement. But there is stress concentration phenomenon. During independent analysis process of gearbox, hanging and assembly, the results of displacement, strain and stress assume certain regularity.