Abstract: The control method for the reactor power by adjusting the beam intensity has been studied for the China initiative Accelerator Driven System(CiADS) facility. In the proposed control method, the beam intensity can be adjusted continuously by changing the aperture size. The aperture size is adjusted automatically based on the PID controllers by comparing the setting power with the measured value. To evaluate the proposed method, a CiADS core model is built based on the point reactor kinetics equation. The simulations based on the CiADS core model have indicated that the reactor power varies with the beam intensity and that the reactor power can be controlled effectively by adjusting the aperture size. Finally, the automatic and manual control functions for the reactor power have been implemented in a Distributed Control System(DCS). In the automatic control function, the measured value of the reactor power is sent to the input-output model of DCS system and is compared with the setting value. Then, the new value of the aperture size is calculated with the PID controller and is sent the drive motor system of the aperture. In addition, the reactor power can also be adjusted by setting manually the aperture size in the control room.