Abstract: An experimental study on fatigue crack growth rate and threshold of WNQ570 base metal and butt weld is performed. Two data processing methods are adopted to derive fatigue crack growth parameters with a 95% confidence level. It turns out that the fatigue crack growth performance of WNQ570 of this batch is excellent, and the fatigue crack growth rate of butt welds is higher than that of the base metal. When the stress intensity is in a common range between 10 MPa·m^1/2 and 70 MPa·m^1/2, the fatigue crack growth rate based on each specimen's data is higher than that based on group method of the data. Furthermore, the fatigue crack growth rate increases and the fatigue crack growth threshold decreases as the stress ratio increases.