Abstract: By using plasma arc additive manufacturing technology, the influence of different process parameters on the microstructure and properties of AlCoCrFeNi_2.1 eutectic high-entropy alloy was studied by the single control variable method. The optimization parameters of the additively manufactured part were obtained to study the influence of different numbers of thermal cycles on the microstructure and properties of the additively manufactured thin-walled parts. The results show that when the melting current is 130 A, with the melting speed at 5 mm/s, and the rotational speed of powder feeding at 2 r/min, a deposited layer with no obvious surface defects, high molding coefficient, and high hardness is obtained. As the deposited layers are stacked layer by layer, the bottom region has the highest number of thermocycling layers, which dissolves the BCC phase into the FCC phase and coarsens the tissue grain, resulting in the lowest hardness at the bottom and higher hardness at the top. The average hardness of the additively manufactured part is 339.70 HV_0.5 ± 4.89 HV_0.5. As a soft phase, the FCC phase shows that the size and the content of its grains decrease from the bottom to the top, which leads to the gradual decrease in tensile strength and plasticity and a slight increase in yield strength. The mechanical properties of the longitudinal specimens are better than those of the transverse specimens, showing obvious anisotropy. The tensile strength can be as high as 1 131.17 MPa ± 34.39 MPa, the yield strength of 594.66 MPa ± 3.71 MPa, and the elongation at break of 16.47% ± 2.21%.