The bottom-up strategy is one of the most important and indispensable restoration approaches for ensuring fast power supply restoration to end users. Reasonably dividing restoration subsystems is an essential step for speeding up the restoration procedure with the bottom-up strategy. Based on the community structure of the complex network theory， a new algorithm for dividing restoration subsystems is proposed. The locations of black-start units and the characteristics of the power grid are taken into account in the algorithm. Then， the modularity index is employed to evaluate the rationality of the division results， and the sequence of interconnecting the subsystems could be determined according to the sequence that every subsystem separates from the system in the divisive process. Some problems existing in the traditional methods， such as how to evaluate the rationality of the dividing results and how to sequentially interconnect the subsystems， could be solved by using the proposed algorithm. Finally， the New England 10-unit 39-bus system is employed to illustrate the essential features of the proposed algorithm.