The work aims to study the fatigue assessment of the welded joints made of high strength steel and treated by high frequency mechanical impact (HFMI) with the structural stress approach and notch stress approach. Based on the research for the nominal stress approach, the HFMI treated test data from four types of welded joint were analyzed by the structural stress approach and notch stress approach. Then the characteristic FAT values for the relevant stress system were statistically proposed. The applicability of proposed FAT values was checked by comparing the values with the relative test data series of welded joints. The characteristic FAT values for the structural stress system and notch stress system was proposed. S-N curve of FAT classes and m=5 varying with the material strength was adopted. The proposed FAT values were in good agreement with the fatigue data for every type of welded joint. For the welded joints treated by HFMI, their fatigue strengths are statistically varying with the material strength. Thus a characteristic FAT value varying along with the material strength should be taken. The excellent properties of high strength steel treated by high frequency mechanical impact can be used fully by the analysis re sults without reducing the safety.