Petri net is a powerful tool for modeling and analyzing systems. It is widely used in a lot of kinds of fields. But there is a problem which bars Petri net development: too much nodes lead to "station explosion", specially when analysing a large and complicated system. How to simplify the Petri net is always an important task for the petri net researchers .This test discusses the union decomposition techenology of Petri net ,and puts forward a new te...