Abstract: Over an extended period, insufficient overall supply of environmental infrastructure has significantly impeded the enhancement of rural ecological environment quality. To investigate the factors influencing farmers' cooperative supply of environmental infrastructure, this paper took decentralized sewage treatment facility as an example, and based on social capital theory, incorporates psychological variables to construct a theoretical model of cooperative willingness. The structural equation model was employed to conduct an empirical analysis of questionnaires collected from 570 farmers in the Guanzhong region of Shaanxi Province, and multi-group analysis was used to examine path differences among farmers with varying annual household incomes. The findings reveal that: (1) Farmers' social capital exerts a significant positive influence on their cooperative supply willingness, and can affect it indirectly through the mediating role of political efficacy. (2) Farmers' cognition significantly and positively influences their willingness to cooperate, and this effect is mediated by value perception. (3) The model shows strong differences across annual household income groups of farmers. Specifically, among high-income farmers, cognition has a stronger effect on value perception, which in turn more strongly influences cooperative willingness. Therefore, in addition to promoting environmental protection concepts, greater emphasis should be placed on fostering rural social capital and enhancing farmers' political efficacy to improve the supply level of environmental infrastructure.