With the increased usage of air filtration and deodorization devices in livestock houses, the demand of agricultural axial flow fans with higher pressure has been raised. To improve the aerodynamic performance of an agricultural axial fan and expand its operating range, a new axial fan was developed using the theory of variable circulation method design via wind tunnel experiments and numerical simulations. The purpose is to change the structural form at the hub of the existing blade to improve the internal flow pattern of the agricultural axial fan, so as to achieve the purpose of improving the aerodynamic performance of the agricultural axial fan and expanding the range of stable operation. In this paper, a new agricultural axial flow fan is designed using the variable circulation method with 0.91m agricultural axial flow fan size and target airflow as design parameters. Secondly, the structural parameters at the hub of the axial fan are optimized by combining the simulation results of the flow field of the designed fan. Factors such as hub diameter d, the placement angle α and the number of moving blades n are analyzed individually, revealing the basic law of the influence of the changes of these factors on the performance of the fan, and the influence of the changes of each factor on the internal flow field of the fan is observed in combination with post-processing. using the better intervals for each factor derived from the one-factor optimisation results, the ventilation volume Q and the energy efficiency ratio N were selected as response values, and a response surface simulation study was carried out for the hub diameter d, the placement angle α, and the number of moving blades n. The response surface simulation study was carried out for the hub diameter d, the placement angle α, and the number of moving blades n. The response surface functional equations were obtained and the better parameter combinations were determined. The correctness of the functional model is further verified by observing the flow field characteristics and external characteristics through post-processing. Finally, the optimised impeller was fabricated by 3D printing technology and wind tunnel tests were conducted, and the results of the actual tests further confirmed the accuracy of the optimisation results. The numerical simulation results of the study show that the optimum combination of these parameters is d=260 mm, α=-0.369°, and n=4 pieces. Experimental test results show that the optimized axial fan performance is better than initial axial fans. On the high-pressure level (120 Pa), the ventilation volume Q of agricultural axial fan increased by 163%, and the energy efficiency ratio N increased by 18.9%. This study proves the feasibility of the variable circulation method in the design of high-pressure agricultural axial flow fan, and the optimization of structural parameters can further reduce the internal vorticity of the fan. The optimized axial fan reduced the secondary flow in the internal flow field, increased the work capacity of the blades, and improved the aerodynamic performance of the fan, ensuring that the axial fan can achieve air circulation and regulation more efficiently in agricultural applications.