Abstract: The mathematical models of docking dynamics in capture process are established for two spacecrafts with inner guide petal peripheral docking mechanisms. Compared with the spacecraft, the initiative capture annulus has much less mass. So its mass and moment of inertia are neglected in the process of modeling, and its geometric character is considered. The contact force is calculated with restriction equation and balance equation. The docking strategy and design parameters of buffer, such as relative displacement, velocity and rotation of docking mechanisms and displacement and rotation of buffer, interacting force are obtained through simulation calculation. An insight of docking dynamics is offered, which is expected to be useful for the design of buffer and docking mechanism.