The invention discloses an expressway road traffic detecting method and device based on a car networking beacon mechanism. The expressway road traffic detecting device comprises a vehicle-mounted broadcast unit, a beacon receiving device A, a beacon receiving device B, a synchronous calibration module, an RS 485 bus, a data processing module, a wireless transmission module, a remote monitoring system and a data storage module. According to the expressway road traffic detecting method and device based on the car networking beacon mechanism, a virtual detecting area is established on an expressway, and the received beacon information is processed in the virtual detecting area to complete the traffic flow detection and the road real-time traffic condition monitoring. The external disturbance resisting capability is high, the device is simple, low in cost and accurate in detection, system maintenance is easy to achieve, the data processing complexity is reduced, the traffic detecting speed is increased, an assisting role can be played on the management of the traffic, and the road condition information can be fast collected and accurately monitored.