At present, the communication infrastructure available in distribution networks makes it difficult to cope with the demand for high data synchronization, and megawatt-level distributed generators (DGs) are mainly connected to the network using the T-connection method. This affects the sensitivity and reliability of differential protection. To solve these problems, this paper proposes an impedance differential protection considering the integration of a high proportion of inverter-based distributed generation. First, a fault component impedance differential protection criterion is constructed by considering the fault output characteristics of DGs during low-voltage ride-through, and the significant differences in the fault component impedance action and braking quantities during external and internal faults are identified. Next, because of the lack of distinct fault component characteristics during severe voltage dips, a positive-sequence impedance ratio magnitude criterion is introduced, specifically designed for high-voltage dips. These two criteria work together to ensure the reliability of the protection system. Finally, a practical distribution network model is established in Matlab/Simulink to verify the effectiveness and reliability of the proposed protection method. Compared with traditional current differential protection, the proposed method alleviates the need for data synchronization, improves the tolerance to transition resistance, and is suitable for scenarios with high penetration of DG.