According to the study on tire load variation when vehicle was running and the relationship of tire load, pressure and temperature, a mathematics model was presented based on the tire load, pressure and temperature. The model could decide whether the tire loads exceed allowable range by means of tire pressure and temperature. By adopting the theory, a tire condition and vehicle load testing system was designed. The system could test vehicle tire temperature and pressure through sensors in the tires. The system decided whether the vehicle was in danger condition and gave suggestions. If the vehicle run exceeding allowable load long time, the system would transfer correlative information to traffic control office through wireless communication networks, thus overload could be avoided. According to the test, the theory was proved to be correct and the system is useful.