Abstract: The design of the flanged joint of natural gas storage and transportation system is based on the criterion of coefficient m, y. However, this kind of connection can not be used to analyze the sealing performance and control the leakage volume. To determine the sealing performance of the flanged joint of a natural gas engineering in Jingbian Project, the new coefficient G b, a and G s, are adopted to compute the leakage rate of pipe flanges of GB series under the condition of the diameter of 15 to 40 mm and the pressure of 0.6 to 4.0 MPa and with the load of standard bolts. The results indicate that the mass leakage rate is 5.81 ~ 10 -6 to 0.37 mg/(s·mm), and the seal quality is in the middle of economy, standard and tightness, and the leakage volume of flange is 5.3 L/d under the condition of the diameter of 40 mm and the pressure of 1 MPa in standard air pressure. In order to enhance the sealing performance, the PVRC method can be adopted to design the flanges by computing the bolt's loads through the mass leakage rate requested.