Early competencies in reading, mathematics, and science are associated with later school achievement and adulthood socioeconomic status. This cross-sectional study examined how fundamental domain-general capacities, including language, spatial, and self-regulatory skills, together relate to competencies in reading, mathematics, and science in young Chinese children. A total of 584 Chinese children aged approximately six years were tested individually on their language (receptive vocabulary), spatial (spatial perception, spatial visualization, and mental rotation), and self-regulation (behavioral regulation and working memory) skills, as well as their academic competencies in reading, mathematics, and science. The results showed that vocabulary, spatial, and self-regulatory skills were all associated with Chinese reading, mathematics, and life sciences, whereas only vocabulary was related to earth and physical sciences. The relation between vocabulary and formal mathematics and that between mental rotation and life sciences were found to be stronger in boys than in girls. The findings suggest that foundational domain-general skills may provide the building blocks for children's academic competencies.