The invention discloses a megawatt-grade broadband impedance measuring apparatus based on MMC, and a control method thereof. The impedance measuring apparatus includes a current disturbance injectionunit, wherein the current disturbance injection unit includes an MMC converter and an isolation branch circuit which is connected with the MMC converter; each phase half-bridge arm of the MMC converter includes one reactor and four sub modules in series; the reactor is connected with the sub modules in series; the isolation branch unit includes a Y-Y type isolation transformer with respective phase change ratio 1; the auxiliary edge of the Y-Y type isolation transformer is connected with an RC circuit in parallel; and each phase original edge of the Y-Y type isolation transformer is connectedwith the corresponding phase bridge arm of the MMC converter. The megawatt-grade broadband impedance measuring apparatus based on MMC satisfies the refinement requirement of a generating equipment simulation model in a new energy generating base, and fills the gap on an accurate measuring method and equipment for high voltage, megawatt-grade and broadband impedance characteristic.