Deep-buried tunnels play a key role in transportation construction, and an in-depth study of their mechanical behavior has important theoretical and engineering practical significance. Considering the spatial variation of the mechanical response of the support structure in deep-buried tunnels and the dynamic relationship between the surrounding rock and the support structure during the construction process, the equilibrium differential equation of the vertical load and radial displacement of the surrounding rock with respect to the change of the tunnel cross-section angle is established. The analytical solutions of the internal forces of the composite support structures are obtained. According to the relationship between support reaction force and radial displacement of surrounding rock, the analytical solution of pressure and displacement of surrounding rock between initial support and surrounding rock, initial support and the secondary lining is deduced. The correctness and effectiveness of the proposed method are verified by numerical simulation and the measured data. Finally, parametric analysis is conducted to investigate the responses of the tunnel by considering such factors as the thickness and the elastic modulus of the support structure as well as the lining installation time based on the analytical method. The results show that the thickness and elastic modulus of the support structure are positively correlated with its bending moment. Compared with the support structure thickness, the elastic modulus has more significant influence on the bending moment. Compared with the secondary lining, the surrounding rock pressure and radial displacement are more sensitive to the changes of the thickness and elastic modulus of the primary lining. The research results can provide the theoretical support for predicting the internal force at any section position of the support structure accurately.