With the high permeability of dc distributed generation and the increasing of sensitive dc electronic load, the flexible dc distribution network is more and more widely used. In order to compare the flexible dc system with the traditional ac distribution system, the flexible dc distribution network planning scheme based on cost analysis is proposed. The optimal location and scale of ac-dc substation, the wiring route of ac-dc feeder and the length and capacity of ac-dc feeder on the middle and low voltage side can be determined by this scheme. The proposed flexible dc distribution network planning scheme is implemented in the region where there is no pre-distribution distribution system and compared with the traditional ac-dc planning scheme. The results show that compared with the ac power distribution system, the flexible dc power distribution scheme can reduce the total cost under sensitive load and improve the permeability of distributed power supply.