Background: Although gender inequality in education is gaining increasing attention, female underrepresentation remains pervasive in STEM fields. Many studies have applied various interventions to narrow the gender gap in STEM education. Objectives: In this study, we conducted a systematic meta-analysis to examine the effectiveness of various interventions for gender equality in STEM education and tested the influence of moderator variables. Methods: Ten databases--ERIC, IEEE, JSTOR, ProQuest-Education, SAGE Journals, Scopus, Springer Link, Taylor & Francis, Web of Science, and Wiley Online Library--and seven high-quality journals in related fields were selected as literature resources. The Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) process was used to identify eligible articles for the random-effects meta-analysis. Results and Conclusions: The overall effect size (Hedges' g) was 0.434, indicating that the interventions promoting gender equality in STEM education had a near-medium positive effect. There were significant differences by the type of intervention, but not by the type of intervention outcome. The results of the moderator analysis showed a significant difference in moderator variables, including country, educational level, form of experiment, intervention level, and different measurement methods, whereas there was no significant difference in the moderator variables, including economic development level and sample size. Implications: This study examined the effectiveness of gender equality interventions and the impact on it of different types of intervention, intervention outcomes, and moderator variables. These results have implications for the design of gender equality interventions in STEM education.