Mining with pressure is one of the effective methods for the coal mining under the threat of water inrush from floor, the group under the coal floor water inrush risk evaluation is one of the important means to ensure mine safety production, and the coal floor water-resisting layer block the determination of water capacity is an important factor of mine water inrush risk evaluation, but the equivalent thickness of water-resisting layer in the water inrush risk evaluation is often difficult to determine effective.In order to assess the equivalent thickness of water-resisting layer, Xinyang mine as an example, from the compressive strength of the lithologic combination, rock formations and waterproof ability and Comprehensive research on the failure depth of floor mining and so on, and finally determine the equivalent thickness of the coal floor of the Ida under the coal floor, for the similar coal mine group under the coal floor water-resisting layer provides a comprehensive evaluation method of determining the equivalent thickness.