During the demolition of a single-tower cable-stayed bridge, the initiation delay time of each blasting incision is determined by the deflection angle of the main tower, and the steel cable of the cable-stayed bridge directly affects the instability and dumping of the main tower due to the complex stress. In this paper, the fixed-axis rotation of the rigid body is combined with the kinetic energy theorem to obtain the functional relationship between the deflection angle of the main tower and the time. Under the condition of satisfying the model similarity theory, the time required for the main tower to deflect each angle is measured by using a high-speed camera. Studies have shown that the deflection of the main tower at 3° takes 3.52 seconds, and the force of the bridge deck acting on the main tower through the steel cable does not exceed 42.15% of its own weight. This conclusion can provide a reference for other projects in the industry.