Abstract: In order to study overburden instability mechanism and strata behavior law of Guojiahe Coal Mine, varieties of methods, such as key strata theory, fracture mechanics, similarity test and field measurement, are used to analyze the instability conditions, rupture forms, weighting characteristics of working face main roof and inferior key layer. Results showed that, in the current mining conditions, main roof occurrs shear-drop instability, and inferior key layer occurrs rotational distortion instability, working-face presents "big weighting" and "samall weighting" characteristics, the reduced mining and caving ratio can effectively decrease the degree of strata behaviors.