For the distribution network connected to the inverter interfaced distributed generation (IIDG), The fault characteristics of IIDG is analyzed, and the fault equivalent model is proposed under the new grid connection regulations. And then, according to the ratio distribution of fault currents at both ends of the faulty line when the IIDG is connected to the distribution network, it is pointed out that the existing current longitudinal protection scheme cannot accurately distinguish between internal and external faults and high investment. A new current longitudinal protection scheme combining main protection with auxiliary protection is proposed, which is combined with the main and auxiliary protection, the auxiliary protection only needs to be configured when the main protection cannot correctly distinguish the faults, and its cost decreased. Finally, A standard IEEE 33?node circuit simulation is set up, and the simulation results verified that the new protection scheme is practical and feasible. It provides reliable protection for the distribution network connected with large number of IIDG.