In order to study the water-inrush mechanism of concealed collapse pillars from the mechanical view,a mechanical model for water-inrush of collapse pillars has been established based on thick plate theory of elastic mechanics in this paper. By solving this model the deformation of water-resistant rock strata under the action of water pressure and the expression of critical water pressure for collapse pillar waterinrush have been obtained The research results indicate that: the boundary conditions and strength of water-resistant strata play important roles in influencing water-inrush of collapse pillars. The critical water-inrush pressure is determined by both relative thickness and absolute thickness of water-resistant strata.