Based on the kinematic characteristics of the ship-based stabilizing platform, the dynamics of stabilizing platform in non-inertial system is investigated and analyzed. By linear-bilinearity formulas of rigid body dynamics, the wrench of the stabilizing platform in non-inertial system are analyzed and the corresponding formulas are given, and the coupling dynamics formulas between the active joint input forces and motions of stabilizing platform are established based on the influence coefficient method. The dynamic model are decomposed into 19 items, and the dynamics characteristics of the stabilizing platform in different sea conditions are analyzed. Finally, the simplifying strategies of the dynamic model in different sea conditions are presented by defining the dynamics influencing factor of wrench applied on the system. It is proved by the numerical simulation that the simplifying strategies improve the computation efficiency greatly and only bring small simplifying errors, and the contradiction between dynamics model complexity and real-time control of the stabilizing platform in non-inertial system is solved.