The invention discloses a coordinated control method for improving a hybrid back-to-back DC system. The method is applied to an inverter station of the hybrid back-to-back DC system of which a flexible DC unit and a conventional DC unit run in parallel; and the method comprises the following steps of: (1) adding a turn-off angle coordinate controller to a reactive power outer loop controller and an AC voltage outer loop controller of the flexile DC unit; (2) selecting the control mode of reactive power outer loop control of the flexible DC unit as the reactive power outer loop controller or the AC voltage outer loop controller according to the judgment result of a fault judgment module; and (3) determining the amplitude limiting size of a reactive current reference value and an active current reference value of current inner loop control of the flexible DC unit according to the judgment result of the fault judgment module. By the coordinated control method, the probability of a commutation failure of the hybrid back-to-back DC system can be effectively reduced; and the AC fault ride-through capability of the system is improved.