Abstract: Taking a composite system of casing-cement sheath-formation in a high temperature and high pressure oil well as the research object,a thermo-structural coupling model is constructed and its theoretical solution is obtained by considering contact,continuity and boundary conditions. The theoretical solution is very accurate in comparison with FEM solution. Comparing the theoretical solutions with thermo-structural coupling effects and without thermal load,it is indicated that thermal load has much greater influence on the equivalent stress. Failure coefficient,which is used to analyze structure integrity,is defined by Mises,Drucker-Prager and Mohr-Coulomb yield criteria. The factors of elastic modulus,Poisson's ratio,nonuniform in-situ stress coefficient,formation temperature and casing pressure are discussed by considering the failure coefficient distribution of casing-cement sheath formation. The results show that the above factors have great effect on the failure coefficient distribution. The failure coefficient of the 1st cementation plane is greater than that of other planes and its influence on wellbore integrity is large.