Abstract: To solve low utilization of DC-link capacitor of mine-used dynamic voltage restorer under long voltage sag, an optimized compensation strategy was proposed, namely a smooth transition between pre-sag compensation and in-phase compensation, so as to restrain aberration of load voltage during the sag, reduce amplitude of injected voltage of dynamic voltage restorer and increase compensation time. The experimental results verify feasibility and reliability of the strategy in balanced and unbalanced grid voltage sag.