The surface of X80 pipeline steel welded joints is processed with laser shock wave, the tensile mechanical properties of the welded joints before and after laser shock processing (LSP) are analyzed with tensile tests. The fracture morphologies and the distributions of chemical components are observed with scanning electric microscope (SEM) and energy dispersive spectrometer (EDS) respectively, and the fracture mechanism of X80 pipeline steel welded joints is discussed. The results show that the X80 pipeline steel welded joints in primitive state have the continuous yield feature, without obvious yield flat, the elongation rate is higher, and the tensile fracture appears the clear delaminated cracking; the strength of X80 pipeline steel welded joints by LSP has not increased, the dimple size and depth become bigger, that improves the tensile properties of the fractures.