Abstract: In medium voltage islanding microgrid, V/f controlled DG（V/f-DG） may produce the fluctuation and collapse of voltage when the support of reactive power only based on the extent of voltage dips. Not only the additional reactive power cannot be absorbed by V/f-DG, but also the active current of V/f-DG is forced to reduce. Eventually, it is possible to bring about the power disequilibrium within network. Thus, according to the typical IIDG control model, this paper analyzed the problem of reactive power reverse caused by the PQ control IIDGs during low voltage ride-through in the case of fault, and revealed the possible adverse effects of this problem on the stability of islanding microgrid. Then, according to the fault characteristics of IIDG, the optimization strategy of master and slave control IIDGs is put forward. Finally, examples are simulated in PSCAD and the results verify the accuracy and effectiveness of the proposed inference and optimization strategies.