To the active-basis-choice decoy-state quantum-key-distribution systems with detector efficiency mismatch,we present a modified attack strategy,which is based on the faked states attack,with quantum nondemolitionmeasurement ability to restress the threat of detector efficiency mismatch.Considering that perfect quantumnondemolition measurement ability doesnt exist in real life,we also propose a practical attack strategy usingphoton number resolving detectors.