Abstract: Excessive application of agrochemicals has triggered serious environmental problems and constrained the sustainable development of agriculture. Exploring the chemical fertilizer reduction effect of high-standard farmland construction is of great significance to guarantee national grain security. This paper constructs an analytical framework, which includes five parts: high-standard farmland construction, soil quality improvement, changes in chemical fertilizer demand, reduction of technical and market risks, and farmers’ decision-making adjustment. In addition, based a survey data of 636 farmers in Jiangxi Province, this paper also analyzes the decision-making logic of farmers’ chemical fertilizer application by the farmers’ multi-objective utility function, explores the impacts of high-standard farmland construction on fertilizer application and its heterogeneity by the OLS and mediation effect models, and furtherly examines the mediating role of operation scale and mechanization level. Results show that, 1) high-standard farmland construction suppresses the chemical fertilizer application in rice production, and every 1% increase in the ratio of high-standard farmland reduces the chemical fertilizer application by 0.153%. This conclusion still holds after the robustness test; 2) The construction of high-standard farmland has a more significant effect on reducing the amount of chemical fertilizers used by non-agricultural households than by part-time farmers with no inhibitory effect on pure farmers. It has the strongest effect on reducing the amount of chemical fertilizers used by farmers in low mountainous terrain, followed by farmers in hilly terrain, while the effect on reducing the amount of chemical fertilizers used by farmers in plain terrain is relatively limited; and 3) The construction of high-standard farmland encourages farmers to expand the scale of operations and improve the level of mechanization, thereby reducing the use of chemical fertilizers. Based on the above results, this paper suggests increasing efforts to build high-standard farmland and improving the management and maintenance system after completion; strengthening the dynamic adjustment of high-standard farmland construction and improving the energy efficiency of the policy; and giving full play to the fertilizer reduction effect of moderate-scale operation and agricultural mechanization.