Abstract: Nets with complex structure are difficult to analyze and control．Reduction method based on characteristic circle may assist in its analysis as its reduced version may be significantly smaller while still retaining the original net’s essential properties．Study of the net is based on single directed graph.On the basis of the conception of connection and path,the circle path and composite circle path were defined．The pure characteristic circle and composite characteristic circle were defined based on conception of characteristic node and common node．The reduction rule and algorithm based on characteristic circle were discussed with samples．The result shows this method can effectively reduce complex net into small parts．However,different sequence of characteristic circle selection may have different reduction result.

Key words: Complex net,Net reduction,Graph reduction,Composite circle,Characteristic circle,Workflow