According to the system requirements, vehicle detection system based on double induction loops has been designed. Control unit of traffic detection system designed with the core of LPC2138 has been described in detail. And the function of each hardware module has been analyzed. For bad experiment environment and various interference factors, anti-interference measures have been considered and introduced into software and hardware design. Hardware implementation and software flow of control unit have been described in detail. The result of the system application shows that, compared to traditional control units with the core of single chip, the control unit have characteristics of better information handling ability, faster speed , and better communication ability etc. The main function of the traffic detection system is to examine the speed, the flow, the vehicle type and the lane occupancy of the motor vehicles. The method based on ARM embedded system in this paper provides a new means for the traffic detection system research. Finally the prospect for further research is presented.