Wind power generation as a clean and sustainable development of new energy has attracted people’s attention. A fan tower is a highly flexible structure, and its stiffness and stability directly determine the performance of fan power generation. The tower barrel generally comprises several conical barrels connected by flanges and bolts. If the bolt connection is loose, there may be a major accident of blade tremor or even blade fracture, which has great safety risks. It is of great practical significance to analyze the dynamic analysis method of tower tube structure. This paper establishes a stiffness model based on a single bolted structure considering contact and bolt preload through static analysis. Then, according to the structure of the fan tower, the equivalent stiffness model of the tower is constructed, which has multiple bolt joint stiffness in parallel and segment column stiffness in series. The influence of bolt loosening on the tower barrel’s stiffness, modal change, and vibration characteristics is discussed using the finite element method. These studies are of great significance for understanding and optimizing the dynamic characteristics of wind turbine tower structures.