In the open-loop distribution network, the reliability can not be increased and the DG can not be connected better. However, in the closed-loop distribution network, the faulty line section can be isolated automatically, the normal line section can be recovered rapidly, and it needs not outage in non-fault zone. So, the civil line and industrial line which form a closed-loop system can improve the utilization rate of equipment and the voltage qualification rate by loads complementary. The maximum short-circuit current value of faulty line is similar between the closed-loop system and the open-loop system, but short-circuit current flows through more lines. The paper proposes the centralized protection to solve the protection problems in the closed-loop operation system. The new distribution network planning principle of using typical connection mode and planning according to the partition, section, load density and load characteristics is given.