Abstract: Blocking infection in the network is a kind of state of network traffic. When blocking happens, how to determine its infected paths or areas and break them off in time is extremely important to the developing of the network ability of transmitting data packets. Also, the decision basis is given for intelligent managing and controlling of networks from their coming research. In this paper, the appearance of network blocking is analyzed and the main words are defined such as key block node, block path, infected path etc. Based on the matrix method of graph theory and the appearance of network blocking infection, a kind of definite arithmetic of infected paths of blocking in the network is given after other similar algorithms are analyzed and compared. The given arithmetic can avoid or reduce the influence the blocking and its infection would have on the network. A means is also given to fix on more blocking nodes and their relation. At the same time, the arithmetic has great practical importance for researching and developing the correlation technology of traffic balancing, scheduling and controlling etc. in the network management realm.