This paper describes the use of mathematical modelling within flap system power driving unit for commercial aircraft. The modelling process is described from the architecture of flap system, the principle and mathematical model of electrical motors and its control loop structure. The model of power driving unit and its external load system are developed in Simulink. Basic retraction and deployment function of flap has been performed, and the response of power driving unit under a typical jam failure of the actuator is provided. This work highlights the advantages of system modelling and simulation to support the load analysis of driveline components (e.g. actuators, torque shafts, etc.) within the conceptual design phase.