Abstract: The effects of extrusion pressure on the microstructure and mechanical properties of AlSi17Cu alloy in the process of squeeze casting were investigated, aiming to provide theoretical support for optimizing the processing conditions of aluminum alloy castings in industrial production. A 200 kN hydraulic press was used to apply three different extrusion pressures of 70 MPa, 100 MPa and 130 MPa for squeeze casting of AlSi17Cu alloy, and the analysis of the microstructure of the alloy was carried out, and the tensile properties, hardness and other indexes were comprehensively determined. The results show that the increase of extrusion pressure has a significant effect on the microstructure of the alloy, especially in the pressure range of 70 MPa to 130 MPa, the size and distribution of primary Si particles and eutectic Si show significant changes. When the extrusion pressure is increased from 70 MPa to 130 MPa, the diameters of the primary Si particles are reduced by 28.4%, the sizes of the eutectic Si particles are reduced by 50.3%, and the grain size of the α-Al phase also decreases by 18.3%. The significant refinement of microstructure contributes to the improvement of the comprehensive mechanical properties of AlSi17Cu alloy. The increase of extrusion pressure can significantly enhance the strength and hardness of the alloy, especially when the extrusion pressure is increased from 70 MPa to 100 MPa, the tensile strength of the alloy increases by 13.9%, the yield strength increases by 22.6%, and the elongation and hardness increase by 19.9%and 9.4%, respectively. However, when the extrusion pressure is further increased to 130 MPa, the tensile strength and elongation decrease slightly, although the yield strength and hardness remain high. This suggests that the increase in extrusion pressure does not enhance all mechanical properties of the alloy linearly, and the ductility of the alloy decreases when the extrusion pressure is above a certain critical pressure.