Abstract: Reviving and promoting green manure cultivation is an effective means of advancing green agricultural development. However, farmers’ transition to off-farm livelihood may adversely affect the adoption of labor-intensive green manure cultivation. Based on a theoretical analysis of the relationship between farmers' off-farm livelihood transition and green manure planting behavior, this study empirically examines this relationship and its underlying mechanisms using microdata of 10 630 rural households in the China Family Database. Results show that off-farm livelihood transition significantly inhibits green manure planting: the greater the extent of the transition, the lower the probability that farmers will plant green manure. This finding remains robust after a series of robustness checks. Heterogeneity analysis indicates that the negative effect is more pronounced among farmers with small-scale operations, labor shortages, and low-profit expectations. Mechanism analysis confirms that off-farm livelihood transition affects green manure planting behavior through human capital constraints and the limited substitutability of production factors. The main contribution of this study is that it systematically reveals the underlying structural tension through which off-farm livelihood transitions impede the adoption of labor-intensive green technologies, examining this tension from the dual perspectives of human capital constraints and factor substitution. It also challenges the simplistic assumption that “capital can perfectly substitute for labor” and provides microlevel empirical evidence for advancing the green transformation of agriculture. Accordingly, this paper recommends improving the agricultural socialized service system, strengthening technical training, and optimizing factor allocation to mitigate the adverse effects of off-farm livelihood transitions and promote green manure cultivation.