In view of the mid-long term voltage stability，an on-line coordinated voltage control strategy based on the segmented-correction model is proposed.The optimal control strategy is solved on-line with the model predictive control（MPC）method.In order to ensure reliable prediction results，the prediction model is modified every time the control horizon is initiated according to the actual measurement information to track the operating state of the actual system.Dynamic load state variable trajectories are linearly approximated within the prediction horizon by referring to the actual measurement information.The differential equations in the prediction model are transformed into nonlinear algebraic equations to avoid dealing with the dynamic differential equations in the optimization control process.A voltage response predictive method for the segmented-correction model is proposed，which transforms the problem solving of the optimal coordinated voltage control model into a tractable mixed-integer linear programming problem.Simulation results show that the proposed scheme can meet the requirement of on-line coordinated voltage control with its capability of coordinating the control of different types and different geographical locations and greatly reducing the calculation burden and time.