Abstract: In an accelerator driven sub-critical system(ADS), it is very important to automatically control the beam intensity of the accelerator. The method for controlling the beam intensity with a proportion-integral-differential(PID) controller has been studied for the China initiative Accelerator Driven System(CiADS) facility. Firstly, in order to quickly find the global optimal parameters of the PID controller, Genetic Algorithm is used for determining the parameters of the PID controller, where the method for initializing the population in the algorithm has been improved. Secondly, a model of beam intensity is built by considering the proton beam with a Gaussian distribution of a given FWHM(Full Width at Half Maximum) at the Low Energy Beam Transport(LEBT) line of the accelerator, in order to evaluate the proposed control method with the extracted PID parameters. The simulations based on the model of beam intensity have indicated that the beam intensity varies with either the different value of FWHM or the different position of beam center. Thirdly, both the automatic and manual control functions for the beam intensity have been implemented in a distributed control system(DCS) system. In the automatic control function, the measured value of the beam intensity is sent to the DCS system and is compared with the setting value. Then, the new values of the aperture size and the rotation angle of the aperture are calculated with the PID controller and are used to adjust the beam intensity. Finally, the accuracy of the rotation angle of the aperture is measured by using the manual function in the DCS system. The measurement results show that the deviation of the angle adjustment of the aperture is less than 0.002 degree, and the adjustment accuracy of the beam intensity is 0.000 05 A.