To address safety problems caused by goaf and water accumulation in open-pit mines, the shallow three-dimensional seismic method and transient electromagnetic method were integrated and applied to detect the mining goaf distribution scope and the water accumulation conditions. In view of the special topographic conditions of an ultrashallow layer and high drop in an open-pit mine, we proposed utilizing bin homogenization and multidomain joint denoising to improve the reliability of seismic data. By using seismic-sensitive attributes to predict the goaf, the transient electromagnetic method was employed to further predict the water accumulation in the goaf. The results show that the shallow seismic method could clearly reflect the reflected-wave variation features of the goaf. The features of a junction between a normal seam and goaf vary obviously, and the prediction effect of the goaf boundary with high resolution is in line with the actual situation. Furthermore, taking the goaf scope prediction with the shallow three-dimensional seismic method as a base, targeted transient electromagnetic detection was deployed, with a detailed analysis of the survey-line repeated areas of the shallow seismic and transient electromagnetic methods. Making full use of the advantages of the shallow seismic and transient electromagnetic methods, we propose a reasonable data interpretation method in combination with the special topographic conditions of open-pit mines, which greatly improves the prediction effect of goaf and water accumulation conditions.