Objective To investigate the effects of ventilation conditions and Daqu stacking methods in the fermentation room on the humidity levels at various points within the room.Methods A three-dimensional unsteady gas-solid coupling model of a small-scale fermentation room is established. Then, the humidity field variation patterns in the room are analyzed using the height of the humidifying air supply outlet (H), the interlayer spacing of fermentation racks (h), and the gap between fermentation piles (δ) as variables. Additionally, multi-objective optimization is performed based on response surface methodology (RSM) and the non-dominated sorting genetic algorithm II (NSGA-II).Results H, h, and δ all significantly affect the humidity field, with h exerting the highest influence weight. Parameter optimization yields the Pareto optimal front: H=492 mm, h=167 mm, and δ=140 mm. Compared with the original model, the humidity regulation rate is increased by 31.9%, and the humidity uniformity index is improved by 11.82% after optimization.Conclusion The collaborative optimization of the fermentation room layout parameters H, h, and δ can effectively improve the regulation of the solid-state fermentation environment, significantly enhancing both the humidity regulation rate and uniformity.