This paper establishes a dynamics model of the axle box bearing of high-speed trains. The model can obtain contact force and its change law. Between rollers and raceway when the bearing contains outer ring faults, inner ring faults, and rolling element faults. Based on the model, the thermal network method is introduced to study the temperature characteristics of axle box bearings of high-speed trains. In this model, the bearing can be divided into some isothermal nodes. The heat generation, conduction, and dispersion of these isothermal nodes can be solved. The results show that the temperature of the contact point between the outer ring raceway and the rolling elements is the highest. By analyzing the relationship between the node and the speed and fault size, it is obtained that the higher the speed, the higher the node temperature. When the fault size increases, the node temperature first increases and then decreases.