To maximize compensating duration during voltage sag， a new time optimal control strategy for voltage sag compensation is proposed. Compared with the traditional control strategies， the proposed strategy can be employed to control the DC link storage energy more effectively under the same condition. By the proposed time optimal control strategy， the maximum compensating time under the condition of lower DC link voltage or lower storage energy can be obtained. To verify the proposed strategy， the new time optimal control strategy and the energy optimal control strategy are compared. The simulation results show that compared with the energy optimal control strategy， under the same condition， longer compensating duration can be obtained by the proposed time optimal control strategy.