The vibration frequency of bridge is the one of important basis for bridge safety. This study adopted the high precision speed meter to measure the nature frequency of bridge, which is received by a self-developed receiver. The multi-hop function of wireless sensor network will be applied to transmit the data into the mid-station. A embedded system saved the data. After the pressure test in the laboratory, the loss rate of data is small than 0.6%, which shows a good receiving rate. If the 12 voltage battery is used, the consuming power of one day is 3 ampere hour in the front station and 30 ampere hour in the mid-station. This system will be applied to estimate the erosion depth of bridge pier by the variation of nature frequency during the flood period.