Abstract: Based on the experimental study on fatigue crack growth of single-welded joint of SA387GR.11CL.12 steel, the curve of the relations between da/dN and ΔK was obtained, which could be used for the safety assessment methods for the pressure vessel with defects. The formula of the curve is da/dN=15.0×10-9ΔK 3.34, whose growth rate is larger than that of the recommended formula from GB/T 19624-2004 as for the same ΔK.Thus the recommended formula from GB/T 19624-2004 was not fit for the safety assessment of the welded structure.