Traditional structural design emphasizes checking whether a loaded structure satisfies design requirements without considering the construction process. There is a great difference in structures between the states in construction processes and design, however. To solve the above problems, a method of nonlinear timevarying mechanics was adopted to analyze the construction process of a structure. The structural characteristics in each construction stage were analyzed by timevarying mechanics and the variations of internal force and displacements obtained. We conclude that designs will not be safe if the time varying effect in the construction process analysis is not considered. We offer advice on the design and construction of largespan structures.