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.