Abstract: AlCoCrFeNi_2.1 eutectic high-entropy alloy is widely utilized in the aerospace, nuclear power, military, and automotive industries due to its exceptional properties, such as high strength, excellent ductility, and remarkable wear and oxidation resistance. However, as the demand for components in the aerospace sector continues to rise, traditional processing methods, such as casting technology, are no longer sufficient for producing complex parts. In contrast to traditional melting techniques, Selective laser melting (SLM), a key technology in metal additive manufacturing, offers advantages, such as precise local process control, flexible design capabilities, and a high cooling rate, overcoming the limitations of conventional manufacturing methods. During SLM, parameters like laser power and scanning speed directly influence the thermal behavior of the molten pool, which in turn affects the microstructure and properties of the AlCoCrFeNi_2.1 eutectic high-entropy alloy. Currently, most studies rely on experimental methods; however, complex thermophysical changes during SLM considerably impact the internal thermal behavior of the component. The temperature field of the molten pool, melting behavior of the powder, and morphology of the molten pool during the forming process cannot be fully studied through experiments alone. Numerical simulation methods offer a more effective, economical, and accurate alternative by reducing the need for experiments. In this study, a finite element model of the AlCoCrFeNi_2.1 eutectic high-entropy alloy formed by SLM was developed using the ABAQUS software, with the movement of the Gaussian heat source implemented through the DFLUX subroutine. The effects of the bath size, temperature change, and liquid phase time on the temperature field, microstructure, and mechanical properties under different process parameters were investigated. By simulating the size and morphology of the molten pool during SLM, the temperature field of the molten pool to produce AlCoCrFeNi_2.1 eutectic high-entropy alloy under various process parameters was determined. In addition, based on experimental observations, the microstructure of the sample was analyzed, and its mechanical properties were tested, confirming the reliability of the numerical simulation. The results show that the maximum temperature and size of the molten pool increase with laser power, whereas they decrease with an increase in scanning speed. The cooling rate of the molten pool increases with the increase of laser power and scanning speed. High-quality AlCoCrFeNi_2.1 eutectic high-entropy alloy samples were fabricated using the SLM technique, with optimized processing parameters of 350 W laser power, 850 mm·s^?1 scanning speed, 100 μm hatching space, and 30 μm layer thickness. The samples exhibited a relative density of 99.7%, with virtually no pores, spheroidization, or warping defects observed. The simulated molten pool width was 138 μm, the depth was 61 μm, and the width-to-depth ratio was 2.26. The samples demonstrated a microhardness of 398.08 HV and an ultimate tensile strength of 1529.5 ± 12.8 MPa, with overall mechanical properties being optimal. This scientific data is valuable for future SLM-based AlCoCrFeNi_2.1 eutectic high-entropy alloy structure design, microstructure evolution, and mechanical property enhancement, contributing to the theoretical foundation for manufacturing high-quality eutectic high-entropy alloy products in industry.