The security and stability of the large scale multi-machine power system is becoming increasingly prominent, especially when severe system faults occur. Active section splitting, as an effective way to prevent the spread of faults, has gradually attracted attention in the power system stability area. In this paper, an improved active section splitting method is proposed. In view of the problems that the existing passive or active splitting technologies always take too much time to calculate online, the splitting section search technology based on multi-layer graph segmentation algorithm in the graph theory is proposed. And the applicability of the proposed method is then verified through the IEEE 39-bus standard test system, which provides a solution for the new power system to quickly deal with the emergency control issues after severe faults and reduce system losses.