Abstract: To set up an effective decision model of process scheduling, the digraph theory was applied. Based on the theory, processing features are expressedwith the vertices of a directed graph, and datum relationships among the processing features are describedwith directed edges. As a resul,t a directed path without a loop and through every vertex in the directed graph is a feasible process schedule. For computer processing of the directed digraph, it is expressed by amatrix, and then the longest directed paths can be obtained through matrices multiplication. If some vertices do not be included in a longestdirected path, these verticeswillbe inserted into the longestdirected path in the lightof the datum relationships so as to obtain satisfied process schedules.