Abstract: Hydraulic fracture is a common geological phenomenon developing in the nature, which plays an important role in the fluid migration, oil and gas preservation and oil-gas safety exploitation. Therefore, this paper, on the basis of in-depth study, defines the generalized concept of hydraulic fracture and points out that the phenomenon of hydraulic fracture is the rock brittleness fracture induced by the increase of pore fluid pressure. Hydraulic fracture includes both tensile rupture caused by the increases of pore fluid pressure and tensile shear and shear fracture also caused by the increases of pore fluid pressure. In this paper, we have used the evaluation method of Retention Press model to acess the risk of hydraulic fracture of the cap rock quantitatively in gas storage of some area.