Abstract: For the peak of relaxation oscillation in the frequency response curves of distributed feedback (DFB) laser,a control system was designed.The system improved the frequency response characteristics of lasers.On the basis of the ageing phenomenon of lasers,the model of lasers was established,and the control system was designed by using H_∞ robust control theory.The frequency response curves of lasers were analyzed and compared under different conditions.Simulation results show that the designed control system can significantly restrain the peak of relaxation oscillation in the frequency response curves,enhance the robust stability of lasers and reduce the influence of parametric disturbance in the system.