Abstract: REDD+ (Reducing Emissions from Deforestation and Forest Degradation plus conservation, sustainable management of forests, and enhancement of forest carbon stocks) aims to encourage developing countries to reduce carbon emissions from deforestation and forest degradation, and to increase forest carbon sinks through forest conservation and sustainable management, serving as an important policy tool for addressing climate change. Based on survey data from Zhungeer Banner and Hangjin Banner in Inner Mongolia, this study employed the propensity matching score method, fuzzy comprehensive evaluation, Logistic regression model, OLS regression, and moderation effect analysis to measure the participation level of farmers and herders in the REDD+ mechanism and to analyze the factors influencing their participation willingness. Furthermore, it discussed the impact mechanism of farmers and herders’ participation on the area of land retired from farming. The results indicated that increasing the level of funding support under REDD+ had a positive effect on expanding the retired farmland area of farming and herding households, with significant differences in participation levels among different farmers and herders. Both age and the proportion of farmland with slopes above 25° had positive effects on the participation of farmers and herders and retired farmland area. In contrast, engagement in agricultural management activities and the farthest distance of farmland from highways had negative effects on both. Village cadres and pioneers of demonstrators in land retirement positively influenced others’ willingness to participate, while education level exerted a suppressive effect. These findings provide empirical evidence for the REDD+ mechanism to reveal the connections and regularities among the environment, economy, and residents’ well-being, and offer path options for formulations of national REDD+ action strategies. Accordingly, due emphasis should be placed on the critical role of farmers and herders in emission reduction and carbon sink enhancement actions, improving their participation mechanisms and refining the subsequent industrial system of REDD+, so as to better serve the national “dual carbon” strategy and the broader goal of high-quality development.