A research was presented to solve the problem of dynamics modeling and characteristics analysis in the case of the mass distribution of the spacecraft changes obviously during the on-orbit propellant refueling process. The variable-mass vehicle was considered to consist of two parts: a rigid platform and the liquid propellant confined in tanks. The liquid in tanks was regarded as a finite number of lumped masses with time-varying mass, configuration and position, so that, the actual physics could be abstracted as a set of variable mass particles with fixed border. Then, the dynamics model of refueling spacecraft was established by using the general equations of mass-varying particles set. Based on some reasonable assumptions about the structure of vehicle, the misalignment moment and the reactive force were eliminated from equations. It is remarkable that the established model include time-varying parameters and damping terms. Besides, the dynamics characteristics of the model were analyzed by using the Lyapunov′s stability criterion. Simulation results demonstrate that the difference structure of the vehicle effect the state trajectories dramatically, and prove that theoretic analysis is correct.