We discuss qualitative reasoning on flow behavior of complex flow networks. Although most of qualitative reasoning methods use qualitative equations, it is difficult to build such equations for complex flow networks, which often appear in the processing plants. We use the flow network itself as a qualitative model, and consider flow behavior based on the topology of the network without using qualitative equations. It is shown that the flow changes can be determined qualitatively when resistance or voltage of a network with a certain topological structure is disturbed at a point. Flows are modeled generally enough to cover from the most ideal of electric current to gas flows and liquid flows.