The access of distributed generations adds new sources to distribution network,which changes the grid structure.The traditional inverse-time overcurrent protection scheme is difficult to satisfy the requirements of selectivity and speed because of randomness of DG’s output power.The digital inverse time overcurrent relay were considered here and a new protection scheme of inverse-time overcurrent protection based on user-defined characteristics was proposed. The proposed protection scheme considers the two relay characteristics constants(A、B) and pick up current、time multiplier setting as continuous variable settings that can be adjusted. The main objective is to minimize the overall time of operation of relays considering the minimum fault current. Four parameters are optimized By using interior-point method to achieve the optimal configuration of the protection.It makes protective relays act instantaneously when fault occurs at line exit end and satisfies the requirements of selectivity and speed. Finally,verification of the protection scheme is carried out by simulation analysis.