Abstract: Generation of reachability graph of Information/solver extended Petri net system(I/S-system) is discussed and the system liveness analysis based on reachability graph is discussed as well.Several definitions relating to system liveness are given.Definition of reachability graph of I/S-system and its generating algorithm are presented.Several theorems about system liveness are given based on reachability graph.At last the example verifies the effectiveness of the algorithm.