Aiming at the frequent lubrication accidents of the high-speed train gearbox,the theoretical calculation of required volume of the gearbox lubrication oil is carried out. The effective volume of gearbox lubrication oil on the specific immersion depth is also calculated by the Fluent. The flow field of the gearbox is optimized,and the effective volume of the gearbox lubrication oil is increased,and the factors affecting on the effective volume of the gearbox lubrication oil are determined. The theoretical calculation of the changing situation of stirring oil loss and the thermal equilibrium temperature of gearbox with the speed under different immersion depths is carried out. The analysis shows that the gearbox structure resistance reduced the effective volume of lubrication oil. The effective volume of lubrication oil and the churning losses of the gearbox increases with the immersion depth increases. The thermal balance temperature rises with the immersion depth increases or speed increases.