Abstract: Storage structure and algorithm are important to Petri net’s simulation and automatization analysis. Petri net is a type of directed graph. Through studying the problem of graph’s storage, a directed graph’s data structure named tree-chain structure is put forward, and its construction algorithm is given. Comparing to other storage structures of directed graph, it can improve the speed and decrease the complexity of the algorithm. The tree-chain structure is very suitable for the application in simulation and automatization analysis of Petri net, so the tree-chain structure of Petri net is emphasized in this paper. Then the generation algorithm of reachability tree based on the tree-chain structure is presented. The tree-chain structure of the reachability tree is beneficial to expanding various analysis algorithms of Petri net.