To address the deficiencies in the research on the dynamic mechanical properties, strain rate sensitivity, and anisotropic characteristics of X80 pipeline steel and its girth welds under high strain rates, as well as to solve the problem regarding the characterization method for the dynamic response of girth welds, X80 pipeline steel and its girth welds were conducted. Quasi-static tensile tests and SHPB (split Hopkinson pressure bar) dynamic compression tests were performed for analysis, the laws governing the material anisotropy and strain rate sensitivity were revealed, and Johnson-Cook constitutive models for girth weld materials with different pipe orientations and welding processes were established. The accuracy of the models was verified through reduction tests. The results show that the quasi-static mechanical properties of X80 pipeline steel exhibit significant anisotropy, with the hoop properties being superior to the axial properties. The quasi-static properties of fully automatically welded girth welds are better than those of semi-automatically welded ones. The axial properties of the base metal are close to those of the semi-automatically welded girth welds but lower than those of the fully automatically welded girth welds. The yield strengths of X80 pipeline steel and girth weld materials fabricated by different welding processes all increase with the increase of strain rate, and the hoop yield strength is slightly higher than the axial yield strength. The yield strength of the semi-automatically welded girth welds is lower than that of the base metal, while that of the fully automatically welded girth welds is much higher than that of the base metal. The quasi-static tensile results inverted by the established Johnson-Cook constitutive models and the restored dynamic compression test results are both in good agreement with the experimental results.