Abstract: Started with measurement of the formation properties,cement and mechanical properties of steel casing in the deformation section in Huabei Jingqiu oilfield,it is proved that the plastic flow of rock Caused by in-situ stress is a main factor resulting in casing deformation,A calculating model of casing deformation is presented and imitaion calculation is conducted with the elastic-plastic finite element soft ware.On the basis said above,several methods to prevent casings from deformation are presented.That has a significant theory guidance.