When interior point method is used to solve the problem of reactive power optimization in large scale power system, the feasible solution may not be obtained because of the unreasonable part of the constraint conditions. In this paper, a practical relaxed reactive optimal power flow method (Relax ROPF) is proposed to restore the solvability of reactive optimization by interior point method. In the iterative process, the ill-condition constraint which causes failure of OPF can be automatically identified, the problem is restored by introducing minimum relaxation into those ill-condition constraints. Test results on IEEE 39-bus system and an actual power grid show that the proposed method can identify unfeasible constraints very well, and can effectively restore the optimal power flow.