Abstract: Baihugou Well is located in the north of Baotou City. Its water level has been observed continuously since 1979. An earthquake measured Ms6.0 occured in Wuyuan County to the west of Baotou on August 25, 1979. Another earthquake measured Ms5.8 occured in Fengzhen County to the east of Baotou on August 13, 1981. In the observation the water levels of this well were all evidently abnormal before these two quakes. Such reliable precursors were offered for the prediction of earthquake.