In order to solve the threat of water disaster in goaf during roadway excavation in Gantang Coal Mine, the transient electromagnetic method was used to detect the whole space, and the resistivity difference of rock strata was analyzed to identify the water abundance abnormal area and carry out water drainage construction, so as to eliminate the influence of water accumulation in goaf on roadway excavation. The practical results showed that the transient electromagnetic method detection indicated that there were significant low-resistance abnormal areas in the roof, floor and bedding direction, and the rock strata in the detection area were generally abundant in water. Through the drainage of the water-accumulated goaf, the cumulative drainage volume was 3 256 m3, which eliminated the threat of water disaster in roadway excavation, and confirmed the effectiveness of transient electromagnetic method combined with drainage boreholes in the control of mine water disaster.