Sex differences in human emotion and related decision-making behaviors are recognized, which can be traced back early in development. However, our understanding of their underlying neurodevelopmental mechanisms remains elusive. Using developmental functional magnetic resonance imaging and computational approach, we investigated developmental sex differences in latent decision-making dynamics during negative emotion processing and related neurocognitive pathways in 243 school-aged children and 78 young adults. Behaviorally, girls exhibit higher response caution and more effective evidence accumulation, whereas boys show more impulsive response to negative facial expression stimuli. These effects parallel sex differences in emotion-related brain maturity linking to evidence accumulation, along with age-related decrease in emotional response in the basolateral amygdala and medial prefrontal cortex (MPFC) in girls and an increase in the centromedial amygdala (CMA) in boys. Moreover, girls exhibit age-related decreases in BLA-MPFC coupling linked to evidence accumulation, but boys exhibit increases in CMA-insula coupling associated with response caution. Our findings highlight the neurocomputational accounts for developmental sex differences in emotion and emotion-related behaviors and provide important implications into the neurodevelopmental mechanisms of sex differences in latent emotional decision-making dynamics. This informs the emergence of sex differences in typical and atypical neurodevelopment of children's emotion and related functions.