More and more tire pressure monitoring devices had been added to vehicle control system, which makes a great contribution to reduce traffic accident. However, most of existing tire pressure detection devices was built in the tire, and it is difficult to repair. At present, only new cars have tire pressure monitoring system, old cars need tire pressure detection system too. In view of the defects of the tire pressure monitoring system and the requirement of the old car to the tire pressure monitoring system, an external pressure monitoring system was designed in this paper. The system was divided into two parts, the detection device and the monitoring device. The detection device is based on the BMP180, a tire pressure detection chip of BOSCH, and it takes the low power Bluetooth chip DA14580 as the controller. The monitoring device takes STM32L152RBT6 as the controller, and the DA14580 is the Bluetooth transmission chip. This system can realize the characteristics of tire pressure, tire temperature realtime monitoring and risk warning, with high reliability, low cost and so on.