Abstract: Based on thedataresultingin thephysical and chemical testsasmadetothe L555M/X80Mand L485M/X70M large-sized LSAW pipes that are used for the Xin-Yue-Zhe,the E-An-Cang and the X pipeline projects,a comparative analysis is made on the chemical composition of the steel plate blank,and the hardness,the tensile strength and the guided-bending test data of the welded joint of the pipe.The analysis result reveals that no softening and weakening pheno- mena are found in the HAZ of the welded joint of the LSAW pipe as made from the steel plate with optimized chemical composition,and used for the Xin-Yue-Zhe project,and that the guided-bending property of the HAZ is also excellent,which means that the performance of the HAZ has been obviously improved.Moreover in the case of the LSAW pipe used for the E-An-Cang project,its welded joint HAZ demonstrates no softening phenomenon,and has good guided-bending property,but shows weakening phenomenon to a certain extent.Likely it is proved that the HAZ performance of the welded pipe has been bettered.