Statistical analyses on fatigue crack growth threshold under three different stress ratios have been done. By the stratified random sampling theory and the weighted least square fitting method, the test data were analyzed based on Paris crack growth rate formulation. The statistical results of the fatigue crack growth threshold under different stress ratios were obtained by linear fitting method. The results show that the fatigue crack growth threshold is influenced by stress ratio R significantly. In the slow crack growth area near the threshold, the increase of stress ratio leads to the decrease of threshold and the increase of crack growth speed. The threshold results under different stress ratios satisfy the normal distribution.