Abstract: AlSi10Mg alloy is an important lightweight material for aerospace and automotive applications. However, the coarse microstructure and internal defects associated with conventional casting significantly impair its strength, ductility, and fatigue resistance. In this study, AlSi10Mg alloy was fabricated by selective laser melting (SLM). By optimizing the SLM processing parameters, specimens with a relative density exceeding 99.5% and a hardness of 130.87 HV were obtained. The fabricated alloy exhibited ultimate tensile strength, yield strength, and elongation of 475.41 MPa: 297.66 MPa, and 6.60%, respectively. Furthermore, the high-cycle fatigue fracture behavior of SLM-fabricated AlSi10Mg alloy was systematically investigated. The results show that the SLM-fabricated alloy is composed of ultrafine α-Al grains and a continuous network-like Si structure, and exhibits a markedly longer fatigue life than its conventional cast counterpart. At a stress amplitude of 120 MPa, the conventional cast alloy fractured after 941,123 cycles, whereas the SLM-fabricated alloy remained unfailed even after 10? cycles. The enhanced fatigue performance is mainly attributed to the ultrafine microstructure and small-scale defects in the SLM-fabricated alloy, which improve fatigue strength and retard crack initiation. Meanwhile, the characteristic network-like Si structure promotes crack deflection and branching during fatigue crack propagation, thereby reducing the crack growth rate. This study provides technical support for the application of SLM-fabricated AlSi10Mg alloy in high-end fields such as aerospace and automotive engineering.