Sectionalizing strategy for the blackout power system could restore the isolated sections of the system in parallel and accelerate the whole restoration process. But the effect of the partition result having on the subsystem restoration is not taken into account in current researches. Due to that it is difficult to establish the partition optimization model considering the subsystem restoration time directly, the optimization strategy based on the rough set theory is proposed, adjusting the partition result achieved by using spectral clustering algorithm. The restoration time duration is the objective function of optimization model and also the index to evaluate the island restorations. The decision table with uncertainty based on rough set theory is used to filter and adjusts the units to achieve the optimal partition result. IEEE 39-bus system and IEEE 118-bus system are used to test the effectiveness of the proposed methodology.