Abstract: The hydro-hazards, water-conductive collapse columns and water inrush from faults, hidden in coal seam floor have caused many coal mines flooded in North China, bringing huge economic losses and safety threats to enterprises. In order to study the hydrogeological effects of the hydro-hazards and hazards locating technology, the sand trough simulation experiments in which the hazard sources are located inside the measurement area are conducted based on the hydrogeological conditions of Carboniferous-Permian coalfields in North China. The experiments show that, when the hydraulic field becomes stable, the effects of collapse columns are manifested by the concentric circles of the water head, temperature and solute concentration contours, with the hazards located in the maximum contour circles. Water head contours are denser in the downstream of the hazard source than those in the upstream, while the contours of temperature and solute concentration are denser in the upstream than those in the downstream. The effects caused by hidden faults present parallel contours, and the hazards are between the two maximum parallel lines. Similarly, the density of water head contours increases in the downstream region of the hazard source, while the density decreases in the upstream region. The temperature and concentration contours are reversed.. The areas constrained by the maximum contours of water temperature and solute concentration for the two hazard sources are much bigger than those constrained by water head contours, and the real size of the hazard sources. Both the sources lay closely to the zone with denser contours. The graphic method and flow-field fitting method to search hazards are proposed in this paper according to the experiments, both of which have an error of no more than 6 m. The technology for hydrogeological effect detection is suitable for detecting water head, temperature and solute concentration in the hidden water-conductive collapse columns or faults in the thin limestone aquifer of Taiyuan Formation presented by Ordovician karst water in Carboniferous-Permian Coalfields in North China, providing a basis for locating and controlling groundwater hazards.