Abstract: To identify optimal mechanical parameters and achieve reliable sealing performances of cement sheath, impact of yield strength, elastic modulus, load of cement sheath on interfacial stress and mode of destruction has been studied, and mechanical adaptability among strength, elastic modulus and load have been reviewed, based on the finite-element mechanical model representing the incorporation of casing-cement sheath-formation, in the creep formation at different well depths. Research results show the cement sheath around wellhead is susceptible to circumstantial stretching with load in casing, whereas the downhole cement sheath is susceptible to yield and high compressive stresses. During loading, cement sheath may have elastic deformation, whereas yield strength of the cement sheath may produce no impact on various stresses on interface. At the same time, various stresses on interface may increase with the increase of elastic modulus. When the cement sheath experiences yield deformation, yield strength of the cement sheath may increase, together with the increase in various stresses on interface. When elastic modulus increases, interfacial contact pressure may increase too, whereas the circumferential stress on internal surface may decrease. During unloading, cement sheath around the wellhead may susceptible to tearing of cementation interface. Generally speaking, cement sheaths have low elastic modulus, moderate yield strength, high tensile strength, and high carrying capacity in high cementation interfacial strength.