The problem of synchronization for chaotic system with mismatch uncertainties was discussed.Based on active control method,an active sliding mode control strategy was proposed,which enables uncertain chaotic systems to reach sliding mode plane within finite time.The stable sliding surface was designed by using linear matrix inequality (LMI) technique to reduce the influence of mismatched uncertainties. The sufficient condition for the existence of stable sliding surface was derived in terms of LMI.The simulation of the synchronization of the systems was presented to show the effectiveness of the proposed method.