The state space explosion problem means that the state space of Petri nets (PNs) grows exponentially with PNs’ size. Even the fundamental reachability problem is still an NP-Hard problem in general. It has been proved that the equivalence problem for the reachability set of arbitrary PNs is undecidable except for some subclass of PNs. That is, the reachability problem of arbitrary PNs cannot be solved exactly. Nowadays, there is no efficient and accurate algorithm to solve the problem.