Under the circumstances of the correctness of conversion rules has already been proved, The first things is conversion the AOE system using transformation rules, and then to do reasonable modifications about the CPN model's unreasonable aspects from two ways. Using these function that acquired by ourselves to get all the reachable paths from the source to sink. In the meantime, we get all the time that all reachable paths have consumed, and the biggest time is the critical path. The method is not only simple and intuitive, but also can improving the execution efficiency under the premise of correctness and rationality, and can reduce the time complexity.