With the access of large-scale distributed generators, the operation mode, power flow characteristics and short-circuit current of distribution network will change greatly, which has a great impact on the reverse-time over-current protection of distribution network lines. Based on the traditional inverse-time current protection of power system, this paper analyses the mechanism and characteristics of the influence of the auxiliary current of distributed generation on the inverse-time protection of distribution network when the fault occurs. And a comprehensive improved reverse-time over-current protection scheme using voltage factor correction is proposed. It meets the requirements of relay protection under the access of distributed generation. A simulation model is established in PSCAD/EMTDC environment to verify the effectiveness of the selectivity and speed of the proposed scheme. This work is supported by National Natural Science Foundation of China (No. 51277143).