In order to improve the feedback stability of flatness control system during the acceleration and deceleration rolling process, the structure and corresponding optimization model of flatness control system have been established based on flatness efficiency factors. Analysis on the work roll bending control loop of the flatness control system has been carried out. Based on the analysis, both the cause of time delay and the corresponding influences on the system stability have been investigated. Moreover, simulations have been implemented for both the conventional PID controller and the Smith predictor-PID controller of work roll bending control with different time delays. Based on the investigation and simulations, a new flatness control strategy including the time delay compensation has been developed. When the time delay varies, the flatness control system will automatically switch the control mode to ensure the system stability is not affected. Applications show that the proposed control strategy can guarantee a good stability and high steady-state precision for the flatness control system during the acceleration and deceleration rolling process.