An optimization model is proposed to give an economical evaluation on different network expansion plans when installing distributed generations (DGs) together with building new lines. The expenditure of construction and maintaining of new DGs as well as new lines, the annual power loss costs are both integrated into the objective function which is to minimize the annual cost of network expansion during planning period. The genetic algorithm (GA) is employed to solve the aforementioned optimization problem. Finally, case studies are carried out on the 3-feeder-16-bus system and a single-feeder-33-bus system as benchmark to demonstrate the validity of the proposed model and method.