Chemistry science popularization for lower grades (Grades 1–2) in primary schools is an important part of science enlightenment education. However, in practice, it generally faces practical dilemmas such as insufficient content adaptability, a single implementation method, and a lack of coordination mechanisms. Based on Piaget’s Cognitive Development Theory and the STSE (Science, Technology, Society, Environment) educational concept, this study constructed a four-in-one strategy system of “content development–teaching implementation–collaborative linkage–guarantee support” through literature analysis, action research, and empirical comparison. An empirical study was conducted in two primary schools for one academic year. The results show that this strategy system can increase students’ interest in participating in chemistry science popularization by 42 percentage points, the compliance rate of observation ability reaches 85%, and the collaborative participation of families, schools, and society rises to 85%. The core strategies formed in the study, including “age-appropriate content screening, interactive teaching implementation, three-dimensional collaborative promotion, and full-process guarantee support,” provide a replicable practical model for the standardized and efficient development of chemistry science popularization for lower grades in primary schools. They also offer empirical references for fulfilling the requirement of “strengthening the pertinence and effectiveness of science popularization” in the Law of the People’s Republic of China on Popularization of Science and Technology (revised in 2024).