Abstract: In the test, fatigue strength of SAF2205 duplex stainless steel welded joints with longitudinal gusset has been studied, hot spot stress concentration factor was computed by the FEM and the fatigue S-N curves of nominal stress and hot spot stress were figured out. Moreover, the test data were statistical treated with the method recommended by IIW and compared with fatigue strength of structural steel with identical joint type. Results show that the test results of duplex stainless steel welded joint with longitudinal gussét obtained by nominal stainless steel welded joint with longitudinal gusset obtained by nominal stress and hot spot stress are FAT136 and FAT163 respectively therefore, is higher than the IIW FAT of corresporuling welded joints in strurtural steel. But there is no obvious effect on the design FAT of duplex stainless steel from its steady load strength classes.