Annular pressure buildup (APB) is generated by thermal expansion of trapped fluids in the closed space of the casing string and threatens the structural safety of the casing string. In the present study a model for estimating deformation of the casing string in cemented and uncemented sections of a pipe based on the theory of elastic deformation is constructed. Calculation of a model of pressure buildup is performed by the method of multistring system analysis. The effect of deformation on pressure buildup is studied and a software application based on the technique of finite elements is used to estimate the deformation of the casing string. The investigations demonstrated that APB calculated with the inclusion of the cemented sections is less than where these sections are not taken into account. Casing deformation affects sections with different levels of the top of cement (IOC) in different ways. For the cemented sections the influence of deformation on pressure buildup is expressed more strongly. Computer verification of the model shows that the range of divergence of pressure buildup does not exceed 3%. Studies of the deformation of the casing string are of practical use in the design of casing strings and in the operation of deep-water wells.