Abstract: A new method of checking the internal leakage flowrate of relief valve was proposed. The theoretical basis of checking the internal leakage flowrate of relief valve by pneumatic measuring instrument was put forward. The experiment results showed that this checking method is accurate and distinct to improve the structure design and the manufacture technology of relief valve. It is of efficiency, low energy consumption　and labor saving for the line checking of the internal leakage flowrate of relief valve as final products.