While the relationship between secure attachment and emotion regulation has been extensively investigated, there is relatively little information about the trajectory of emotion regulation in childhood and whether changes in emotion regulation would mediate the relation between mother-child secure attachment and independence. A latent growth mediation model was tested using data from the 'Kids in Taiwan', a national longitudinal project on child development and care in Taiwan. All participants (N = 1181, 49.5% boys) are Chinese. The results revealed that (1) the growth trajectory of emotion regulation increased rapidly from age 4 to age 6 in children; (2) the trajectory of emotion regulation mediated the relationship between secure attachment at age 4 and subsequent independence at age 6. These findings provide further evidence that early childhood is a vital period for children's development of emotion regulation, and secure attachment is an important factor in supporting long-term emotion regulation and independence in childhood.