We propose a simple PID (proportional integral differential)-I controller to improve the performance of a CCD-based (charge coupled device) control system for fast steering mirror, which consists of adding an integrator in series to a PID controller, resulting in two integrators in the control loop. The conditions for implementing the PID-I controller into the control system of the fast steering mirror are presented mainly in terms of the closed-loop stability and error attenuation. A model of CCD-based control loop is made to analyze the characteristics of the control loop. Although the error attenuation bandwidth with PID-I controller is a little smaller than that with an integral controller, the error attenuation at low frequency is greatly enhanced. The experimental results are in accordance with the theoretical analysis.