Abstract: Strengthening the post-construction maintenance of high-standard farmland is essential to ensuring its long-term benefits. As the main users and direct beneficiaries of high-standard farmland, farmers’ maintenance behaviours play a vital role in determining the effectiveness of farmland construction. Based on 474 survey samples of farmers in Jiangxi Province, this study employs the Heckprobit model and mediation effect model to empirically analyse the impact of social capital on farmers’ participation in high-standard farmland maintenance and its mechanisms. The results show that: 1) Social capital significantly promotes farmers’ participation in high-standard farmland maintenance. The richer the social capital, the higher the farmers’ willingness to participate, and this conclusion remains robust after testing; 2) Mechanism analysis indicates that social capital enhances farmers’ social responsibility perception and facilitates land transfer, thereby further encouraging their participation in maintenance; 3) The effect of social capital exhibits heterogeneity across farmers with different resource endowments. For farmers with stronger grain production capacity, confirmed farmland rights, and higher educational levels, the promotional effect of social capital is more significant. Based on these findings, it is recommended to improve the cooperative management system of high-standard farmland, build a long-term maintenance mechanism characterised by active farmer participation and multi-party collaboration, and provide practical references for improving maintenance efficiency and consolidating construction achievements.