The wellbore instability of Jinzhou 25-1 oil field is quite serious. In order to decrease wellbore instability of the oil field, the clay mineral of shale is identified by the X-ray diffractometer. Laboratory experiments involving the rock mechanics and hydration characteristics of shale are conducted to study their rock mechanical characters and wellbore instability mechanism. Shale in Shahejie Formation has two types: they are bedding shale and water-sensitive shale. Strength of bedding shale is anisotropy, and is prone to shear failure along the bedding plane and causes wellbore instability. Water-sensitive shale would be hydration swelling under the action with drilling fluid, resulting in the change of mechanical properties around the well, showing a changed collapse pressure with the time. Based on the experimental results, the methods to determine collapse pressure are developed, which is applied to determine collapse pressure of Jinzhou 25-1 oil field, and engineering strategies for ensuring safe drilling are given. Based on optimized well trajectory and proper drilling fluid density, the problem involving the wellbore instability of the oil field is able to solve by increasing the plugging and inhibitory of drilling fluid.