To help the planning and design of distribution automation systems (DAS), the service area is classified into six types. The technologies of distribution automation, such as, the host systems, the terminal units, communication systems and relay protections are discussed and cataloged. It is suggested to determine the mode of the host systems according to the scale of the city. The specific planning principle of implementing the terminal units, communication system and relay protection in accordance with the type of the area is proposed. Based on the static data of service reliability for rural customers in China, the feasibility and effectiveness of the proposed specific planning principle is analyzed. A middle scale city with 590 feeders is given as the example of planning to demonstrate the proposed method in detail.