An optimal setting method of inverse time over-current protection for distribution network with DGs（Distributed Generations） is proposed. Taking the minimum total operation time of main protection and backup protection as the objective function and considering the constraints such as the selectivity

the mathematical model of protection optimization is established. By setting the dynamic parameters and introducing the optimal weight

the HSA（Harmony Search Algorithm） is improved in aspects of convergence speed and the ability to obtain the global optimal solution.The mathematical model of protection optimization is solved by the improved HAS. The optimal setting parameters are obtained based on the short circuit currents from different fault points in distribution network and the contribution of DGs is considered in short circuit current calculation

which makes the optimal setting results applicable to the distribution network with DGs. The off-line protection optimization is carried out respectively for the two-phase short circuit fault and three-phase short circuit fault

and the optimal setting parameters are selected automatically and real-timely according to the different fault types

by which the defect that the protection is easily affected by fault types can be overcome. Simulative results show that the proposed method can effectively improve the selectivity and speed of the inverse time over-current protection for distribution network with DGs.