Facing the environment degradation brought about by greenhouse gas emissions and energy crisis，all researches with energy-saving and low-carbon as the theme have won a lot of public concern.As network power loss plays an important role in low-carbon energy，from the point of system planning，new methods and approaches have been proposed for its reduction from the perspective of system planning.First of all，the generalized concept of reactive power demand for network buses is proposed.Based on the load flow model，virtual reactive power sources are deployed at some bases concerned to make their voltage controllable.An optimum model with the objective to minimize the network power loss and the values of those voltage magnitudes of controllable buses.To solve the optimum problem，a hybrid method involving particle swarm optimization and power flow is proposed.With the help of the hybrid method one can establish the reactive power demands at network buses.The data of the typical operation mode of Shandong power network is used to analyze the scheme for the optimum reactive power compensation for the target power grid.The rate of decrease of power loss is compared between the initial specific operation mode and the optimum mode.It is expected that the work done can be useful as a reference to planning of reactive power equipment in the power grid.The method proposed is successfully used in engineering and research projects.