In this study, cadmium (Cd) isotope labeling of pollution sources and dual-isotope composition experiments for homologous Cd were employed to establish a quantitative tracing model for Cd sources in Folsomia candida (springtails) and to investigate the influence of factors such as pollution levels and dietary differences on the contribution of Cd sources in springtails. The study successfully developed two-source and three-source quantitative models for Cd in springtails. The results showed that in the dual-source system (Cd solution and food), under low Cd concentration treatments, both adults and larvae primarily accumulated Cd from food sources (85.0% and 64.6%, respectively). As pollution levels increased, the contribution of Cd from the solution source rose from 15.0% and 35.4% to 43.0% and 73.9%, respectively, with larvae consistently exhibiting higher solution-source contributions than adults under equivalent treatments. In the three-source system (Cd solution, straw, and saprophytic fungi), springtails selectively fed on saprophytic fungi, even when Cd concentrations in fungi were significantly higher than in straw, regardless of pollution levels. This indicated that the preference of Folsomia candida for food resources has a more significant impact on its Cd source than the level of food contamination. The findings of this study provided theoretical insights for blocking heavy metal uptake in soil fauna and remediating contaminated soil ecosystems.