Based on multiple astronomical observation results, this paper proposes the hypothesis of the principle of relative change in the speed of light and demonstrates its compatibility with the principle of the invariance of the speed of light. The study shows that the speed of light has both an absolutely constant aspect and a relatively variable aspect. This provides us with a new direction to study the relationship between the relative change in the speed of light and the motion of matter. Based on this principle, the paper constructs an innovative theoretical framework known as the "vacuum dynamical mechanism" and derives several important conclusions. The research finds that time, space, and the speed of light always maintain a proportional relationship. The relative change in the speed of light leads to the formation of high-energy spaces, low-energy spaces, and variable-energy spaces. In the variable-energy vacuum space, objects spontaneously accelerate towards low-energy regions. The acceleration gained by an object is only related to the rate of change of the speed of light in space and is independent of the object's mass. The vacuum dynamical theory proposed in this paper offers a new perspective for explaining the origin of dark energy and the physical mechanisms behind spacetime curvature.