This paper gives a method of chaos control to acousto optical bistable (AOB) system using the technique of continuous parameter delayed feedback. Numerical results show that under some stiffness of control the controlled system has negtive maximum Lyapunov exponent (MLE) in the initial chaotic domain and so that controlled state is convinced to be the unstable fixed point or unstable periodic orbit (UPO) of the initial system. By comparied with the experimental results, the validity of this control method is verified.