Abstract: After the inverter interfaced distributed generation(IIDG) is connected, the distribution network becomes a complex multi-source system, which also changes the traditional power flow structure, operation mode and fault characteristics of the distribution network. Taking advantage of the positive factors of IIDG access to protection, the active action mechanism of IIDG grid-connected inverters is constructed. A harmonic differential protection scheme for distribution network with IIDG based on characteristic signal injection is proposed, which makes the protection more flexible through the active participation of IIDG. Constrained by the power quality of the IIDG PCC point and the output power limit of the IIDG, the characteristic high-order harmonic signal is injected into the inner current loop of the IIDG, and the activation time and effective period of active signal regulation are determined. Based on this, the harmonic current content differential protection scheme is proposed, and the rationality of the proposed protection scheme is verified by simulation.