The barrier properties of packaging material play an important role in food and pharmaceutical packaging. Up to now, differential pressure method has the longest application history in barrier properties testing and been used in worldwide. With the development of testing and highly accurate pressure sensor technology, differential pressure method has become much more consummate than before. But there are still the doubts that differential pressure maybe has some influence on film structure finally on permeability. In order to clear this effect, this article will explain the relation between differential pressure and barrier properties based on the actual test data.