<p>Titanium alloys are extensively used in aerospace applications, where dwell fatigue can significantly reduce the service life of aircraft engines and potentially lead to accidents. This is due to the deformation incompatibility between soft and hard grains in titanium alloy, which notably affects the nucleation of dwell fatigue cracks. Slip transfer across grain boundary (GB) is a crucial mechanism for accommodating plastic deformation at the GB interfaces. However, the specific role of slip transfer in dwell fatigue crack nucleation is not yet fully understood. A dwell fatigue crack parameter (<i>DF</i>) is proposed in this study, based on the slip transfer effect, incorporating the grain size of the soft grain, the maximum prismatic Schmid factors of the soft grain and the portion of the Burgers vector of the dislocation residual at the GB. Our findings suggest that larger soft grain size and Schmid factor exacerbate dislocations pileup at the GB, while a greater angle between slip directions on either side of the GB amplifies the residual dislocation magnitude. The combined influence of these three factors impacts slip transfer and dwell fatigue crack nucleation. When the <i>DF</i> value is greater than 3, severe strain localization occurs at the GB, increasing the probability of cracking. This study offers valuable insights for quantitatively analyzing slip transfer in relation to dwell fatigue crack nucleation and the prediction of fatigue performance.</p>