The pneumatic oneway valve is a pneumatic component which flow area changes with the change of the inlet pressure. Its flow characteristic parameters cannot be measured by using ISO-6358. But as a result of check valve fully open pressure is low, and the critical pressure ratio b is bigger, so constant pressure method,variable pressure method and concatenated method can be used to measure its flow characteristic parameters. In the case of known S and b,how to obtain the flow qv through the check valve at any pressure difference p1－p2 was shown.