Abstract: Amid large-scale population mobility, young people of reproductive age increasingly move across regions, reshaping their fertility environment and decision-making processes. Using data from the 2021 Chinese General Social Survey (CGSS), this study examines how mobility affects youth fertility intentions and explores the underlying mechanisms. Multiple linear regression and instrumental variable approaches are employed for empirical analysis. The results show that migrant youth exhibit significantly lower fertility intentions than their non-migrant counterparts. Mobility has a stronger dampening effect on fertility intentions among men than among women, among rural youth than urban youth, and among those with higher levels of education than those with lower levels. Further analysis suggests that mobility reduces fertility intentions through three pathways-survival pressures, life-course disruption, and social integration. First, migrant youth often face substantial economic pressures and must devote more time and energy to the labor market, intensifying work–family conflict. Second, mobility disrupts established life trajectories, making partner matching more difficult and delaying the age at first marriage. Finally, as migrant youth integrate into their places of employment, traditional family norms tend to weaken, further lowering fertility intentions.