The geomagnetic vehicle detection system uses the detection of geomagnetic changes to obtain relevant traffic information. In view of the actual problems of existing geomagnetic vehicle detection equipment, such as baseline drift, unstable correct detection rate of traffic flow, and equipment mis-detection caused by environmental interference, a geomagnetic vehicle detection system based on finite state machine is proposed. The system uses magnetic sensor to collect the original signal of magnetic field, pre-process the original signal by embedded program. The upper computer adopts the algorithm based on the judgment of the state machine to divide the vehicle detection process into several states, including no vehicle, initial change of waveform, quasi-entering, vehicular, quasi-leaving and waveform stabilizing six states. In order to improve the accuracy of detection algorithm, corresponding tasks are performed in each state, including baseline tracking and updating, sampling point counting and so on. The accuracy of the detection algorithm is over 97%.