Abstract: This paper analyzes the casing failure mechanisms of oil and water wells in Daqing Oilfield, concludes that the fundamental factors resulting in casing failure are the water entering into the shale of the marked bed and the forming of a certain immersion area.This paper introduces the fundamental measures for preventing and slowing down the casing failures:prevent water from entering from non oil reservoirs, regulate and control differential pressure in well patterns, reasonably control water injection pressure, prevent the forming of high pressure and holding back pressure layers and so on. The implementation of the above protective measures has reduced the casing failure wells from 315 in 1986 to 225 at present.