Abstract: The hydrofracturing data in the Fuyu oil field were used in the analysis of stress in the oil field, and the cause for the deformation of casing was discussed. The action of horizontal compress-stress plays a leading role in this region. Due to high pressure water injection, the effective normal stress is decreased, and this sets off the relative slide between the rock layers and resulting in the deformation of casing. The major deformation of casing is caused by slipping along the horizontal boundary surface AB.If the pressure of injection and the mode of water-injection can be controled, it may be possible to decrease the pore pressure of the AB boundary surface and the normal stress at the boundary surface can be restored and the rate of casing deformation can be decreased.