In this paper, we for the first time propose a dynamical system (DS) approach to describe the evlution of passenger trips over time in scheduled express service. The analysis and model of this dynamical study is of several advantages. First, it can be used for dynamical analysis, such as quantitative, stability, and equilibrium analysis. Second, it can be further applied to analyze the competition behaviors among various operators in the coach industry. Under some proper assumptions, the ordinary differential equation (ODE) model is formulated together with the collected data to describe the passenger variation. We solve this first order ODE with an analytical technique, and find the result fits the collected data. Some concluding remarks and future works are also suggested in this work.