Abstract: The interrelation of static fatigue S-N curve and vibration fatigue S-N curve on Q235 B steel butt welded joints has been analyzed. The result shows they have the same slope, and vibration fatigue S-N curve is a continuous curve without horizontal section. It moves a specified distance in stress axis. At the same time, the vibration fatigue S-N curve expression was input. In this paper, the static fatigue test and tensile test under different load frequency were done. And vibration fatigue correction factor was 0.345 2. Through correction of residual stress and size, the fatigue limit was 114.84 MPa when the cycles were 5×10⁶ under vibration fatigue S-N curve. And it only has a little bias 7.60%, it shows that the method of this paper can be used to infer vibration fatigue S-N curve of Q235 B steel.