Farmers are central local actors in agricultural heritage conservation, and understanding the decision processes underlying their participation is essential for long-term and effective conservation. Using the Shexian Dryland Stone Terraced System, a Globally Important Agricultural Heritage System, as a case study, this study develops an integrated stakeholder-Theory of Planned Behavior (TPB) framework. Economic benefits and government support are modeled as external antecedents, and structural equation modeling is used to test how these antecedents, the core TPB constructs, participation intention, and conservation behavior are related. The results show that subjective norm showed the strongest association with participation intention; economic benefits have significant indirect associations with participation intention and self-reported conservation behavior through the core TPB constructs; and government support has the largest estimated total association with self-reported conservation behavior, exceeding the estimated association between participation intention and self-reported conservation behavior. The study extends the application of TPB to agricultural heritage conservation and identifies key modeled pathways associated with farmers’ participation, providing policy-relevant empirical evidence to inform efforts to strengthen farmer participation in heritage conservation.