A new efficient heuristic algorithm of O($\mid{V}\mid\cdot\mid{e}\mid$) for network partitioning via the concept of connection index of weighted graph is presented, where $\mid{V}\mid$, $\mid{e}\mid$ are the number of vertices and edges, respectively. And the schemes for making the associated graph for node tearing analysis and IC layout are considered. The experimental results show that our algorithm is very efficient and yields near optimal solutions. Finally two applications of the network partitioning in CAD are presented. One is general diakoptic analysis and the other is decomposed topological analysis.