Abstract: In order to analyze the instability rule of protection water soil layer influenced both by stress and seepage field,the effective stress principle and elliptic arc sinking fitting curve are used to theoretically analyze the stability of protection water soil layer,and get the discrimination formulas;based on the planar solid-liquid coupling experiment platform,the high precision water quantity monitoring and infra-red image monitoring technology are adopted to test roof water-inrush disaster in shallow coal seam,verified the theoretical judgments,and revealed the two laws of destroy instability at the same time. The study shows that in the case of thin bedrock,the instability of protection water soil lay-er closely contacts with mining parameters,which leads to disasters during two mining periods-open-off cutting and pe-riodic weighting periods of working face. Tc of former is smaller forming a “rivet type shear failure”,while,the latter is larger forming an “elliptic arc tensile fracture”. The reveal of two failure modes provides a reference of prediction on roof water-inrush disaster in shallow coal seams.