Taking into account the complex and the lack of load data of actual distribution system, this paper establishes a simplified model of distribution network based on the equivalent load which can reduce the calculation time and reflect the flow distribution of the distribution network. A service restoration program for complex distribution system with distributed generation is proposed. When serious failures result in large area power blackout, the best supply area of the island is determined when the distributed power supply capacity is known and DG switches to the islanding operation mode to maintain the power supply for the important load. Then the remaining network loss of power is restored based on heuristic rules and optimized with the improved branch-exchange algorithm to make the loss of power load and network loss as little as possible. At last, the simulation results of the example show that the method can effectively solve the problem of distribution network service restoration.