Abstract: Farmland consolidation has been widely used as the engineering approach under the mechanization and agronomic practices in hilly and mountainous areas. Farmland consolidation suitable for agricultural machinery can be expected to improve farmland use efficiency and stabilize grain production and high-quality agriculture under terrain constraints. However, the parameter design of farmland consolidation is often required to balance the conflicts among agricultural machinery, terrain adaptability, engineering cost control, and ecological security under complex topographic and ecological constraints. However, the existing design can rely largely on empirical approaches or single-objective optimization in practice. It is very necessary to consider the agricultural machinery and ecological security. In this study, a parameter design was proposed to evaluate synergy between production and ecology in farmland consolidation suitable for agricultural machinery. A case study was taken from the typical farmland consolidation area in Gujiao City, Shanxi Province, China. High-resolution topographic data was acquired using drone imagery. A digital elevation model (DEM) was generated to accurately extract micro-topographic features. Reliable data support was provided for plot parameter design. The requirements and hilly terrain features were integrated to determine the key indicators (including agricultural machinery operation suitability, terrain adaptability, and ecological constraints). A plot parameter design system was obtained after evaluation. A multi-objective optimization was established to minimize the excavation and filling volume, plot slope, and shape index. The constraints were related to the machinery operation, soil and water conservation, and engineering feasibility. The multi-objective particle swarm optimization (MOPSO) algorithm was introduced for efficient solving. The Pareto optimal solution set was successfully obtained for the trade-off mechanisms and synergy paths among the objectives. The technique for order preference by similarity to ideal solution (TOPSIS) was then applied to evaluate the Pareto solutions and then identify the optimal combination of the parameters. The results showed that the six schemes of parameters were obtained for farmland consolidation suitable for agricultural machinery. Among them, the high performance was achieved in the 7-stage terrace scheme (N7) with the Natural Breaks method. The parameter combination included a plot shape index of 1.58, an average plot width of 27.16 m, a plot slope of 9.95°, and an excavation and filling volume of 42790 m³. Compared with the pre-consolidation conditions, the shape index and plot slope were significantly reduced by 57.9% and 23.2%, respectively, whereas the plot width increased by 70.2%. The continuity was verified in the agricultural machinery and terrain adaptability. Engineering costs were effectively controlled to minimize the ecological disturbance. The plot parameter design was combined with the MOPSO–TOPSIS optimization. The optimal synergy of "production-ecology-economy" was achieved in the farmland consolidation suitable for agricultural machinery. The parameter design and optimization framework can be expected to resolve multi-objective conflicts in farmland consolidation suitable for agricultural machinery in the hilly and mountainous areas. The findings can also provide quantifiable and generalizable technical references on the multi-objective decision-making for production efficiency and ecological security.