The influence of load self-start on the over-current protection of distribution network when external fault removal, a new principle of adaptive over-current protection based on current mutation is proposed. By using the significant differences characteristics between the current of lines in the process of distribution network internal fault and fault removal, it realizes the accurate identification of load self-starting process. When the current mutation is detected greater twice successively than the set threshold value, and meets two criterions, the load self-starting process can be determined. An overcurrent protection setting method is proposed, which can be dynamically adjusted according to the load change, so as to build an adaptive over-current protection scheme. The simulation results show that the new principle of adaptive overcurrent protection based on current mutation is effective and practical. The principle is free from the influence of load self starting and load change, which can effectively increase the protection range of the backup protection and ensure the reliability and sensitivity of the protection. This work is supported by National Natural Science Foundation of China (No. 51477090).