In control system research, the pendulum system is one of the important nonlinear systems, and it has been widely used in many control applications. Different from the conventional pendulum system, this paper presents a reaction wheel based pendulum control system. From the application point of view, the design task is to stabilize the pendulum system through the reaction force generated from the flywheel. To this aim, dynamics modelling of the reaction wheel based pendulum must be considered first. Second, the system parameter identification scheme is required for future controller designs. Therefore, in this paper, dynamics modelling of the reaction wheel based pendulum is derived in term of Lagrange equation. For the associated nonlinear model, a discrete model approximation is proposed for the identification of system parameters. Finally, simulations are carried out to demonstrate the feasibility and effectiveness of the proposed method.