At present， both at home and abroad are facing serious casing damage problems， so it is necessary to study the influencing factors of casing strength. By establishing a three-dimensional finite element model of casing and cement sheath， and using Ansys finite element analysis software to study the influence of cement sheath parameters， casing eccentricity and ovality on casing strength. The simulation results show that only when the elastic modulus of the cement sheath exceeds a certain value， increasing the thickness and elastic modulus of the cement sheath can improve the strength of the casing， otherwise the equivalent stress of the inner wall of the casing will be increased， and the effect of the cement ring on the strength of the casing is a function of the diameter-thickness ratio of the casing. In addition， the strength of the casing decreases significantly with the increase of the eccentricity and ellipticity of the casing， which can easily cause yield failure of the casing.