Abstract: During the welding process of welded structures composed of steel pipes， typical volumetric welding defects such as porosity are easily formed， which may result in high-cycle fatigue failure of the structure under low-amplitude cyclic loads. Therefore， based on a combination of experimental and numerical simulations， the paper studied the effect of porosity defects on the high-cycle fatigue life of welded steel pipe specimens. First， two groups of steel pipe weldments with intact welding and porosity defects were designed for high-cycle fatigue tests； then a simulation model of porosity weldments was established and verified based on the test results； finally， the influence of different axial directions， circumferential directions， and radial dimensions of porosity defects on the stress concentration factor and high-cycle fatigue life of steel pipe weldments was analyzed using the simulation model. The results showed that the three-dimensional size of porosity defects exhibited different influence mechanisms on the stress concentration and high-cycle fatigue life of steel pipe weldments. Since the size of the welded pipe wall was much smaller than the other two directions， the stress concentration and high-cycle fatigue life were most sensitive to the radial size of the defect， casuing drastic variations in stress concentration and significant reductions in high-cycle fatigue life； because the increase in the axial size of the defect did not reduce the effective bearing area of the section but decreased the specificity of the defect shape， the stress concentration factor decreased with the increase of the axial size of the defect， thereby maintaining a long high-cycle fatigue life； since the increased circumferential size of the defect reduced the effective bearing area of the section， the stress concentration factor increased with the increase of the defect's circumferential size， thereby decreasing the high-cycle fatigue life to a certain extent.