There are always network nodes that can cause widespread blackouts in the built power system network, which are called weak links. Thus seeking the weak links in the network has an important significance to a large power system network. The new algorithm model based on node power variation and the small-world network model for regional power system can estimate the effect on other elements power when the power of generation node changes or splits from the grid. Then through proposing the concept of the power change degree, the weak links in the power system could be identified and theoretical support for economic and reliable construction of the power system is provided. In the end, the validity of the new algorithm is verified through an example of the power system.