Encouraging public participation in waste classification is of significant importance for the advancement of sustainable societal construction. This paper employs an exploratory sequential mixed-methods approach to investigate the mechanisms underlying public engagement in waste classification. Study one, through field interviews and surveys, identifies waste classification knowledge and perceived behavioral control as the primary factors influencing individuals’ engagement in waste classification. Study two employs quantitative methods to validate the model and further examines the relationship between public and private domain waste classification. The results indicate that waste classification knowledge indirectly and positively predicts private domain waste classification through perceived behavioral control; waste classification knowledge negatively predicts private domain waste classification through its negative impact on public domain waste classification; and waste classification knowledge influences private domain waste classification via the serial mediation of perceived behavioral control and public domain waste classification. This study extends the understanding of factors affecting waste classification, clarifies the relationship between different types of waste classification, and identifies perceived behavioral control as a key variable in translating knowledge into waste classification actions, which has educational and guiding significance for promoting public adherence to waste classification practices.