Distributed resources (DR) have important impacts on power loss of distribution network system, including the location, capacity and power factor of DR. Based on radial single circuit network and uniform distribution constant power load model, the mathematical relations between reduction of power loss and location, capacity and power factor of DR were deduced for single DR inserting, and generalized for multiple DR inserting. The optimum location and capacity of DR were obtained. The influence of DR inserting on the power loss of distribution network was simulated and analyzed. The conclusions investigated in this paper provided theoretical references to optimal operation mode and power network planning of DR.