The gasket is a key sealing element in the bolted flange connection system.When measuring the leakage rate in the laboratory,rigid flanges are usually used to load uniformly through the testing machine.However,the effect of bolt tightening method in production practice on the leakage rate is ignored.The effects of the cross tightening method,sequential tightening method and legacy star pattern tightening sequence in ASME PC-1-2013 standard on the stress of gaskets were studied by the numerical simulation method.The three tightening methods were compared with the uniform tightening method.The results show that the bolt preload is not uniform for all the three tightening methods.The legacy star pattern tightening sequence has the best preload effect and is closest to the preload effect of the uniform tightening method.Under the same load,the stress on the gasket is different under different tightening methods.Considering the heterogeneity of the stress distribution of the gasket,the existing formula for predicting the leakage rate was modified,and the modified formula was verified by the test.The results show that the leakage rate predicted by the modified formula is more consistent with the experimental result than that predicted by the existing formula.The research is of great significance to improve the accuracy of leakage rate prediction of the bolted flange connection system.