Correlation of stress intensity factor and defect size for welded joints of high-speed train bogie frame was analyzed and calculated by means of fracture mechanics principle for surface linear defect and root continuity defect. More specific results were thus provided on allowable defect size under different stress range based on material properties of welded joint. Results show that stress intensity factor of crack tip increased with flaw depth and stress range, but decreased with the ration of depth and semi-length.Furthermore,flaw tolerance depth was significantly reduced with the increase of stress level.