The phase structure, microstructure and mechanical properties of Fe_46-xNi₂₀Co₂₀Cr₁₀V₄Al_x (x=5, 8, 12, 15) high-entropy alloys with different Al contents (atom fraction, %) were systematically investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and performing uniaxial tensile test. The results show that with the increase of Al content, the phase structure of Fe_46-xNi₂₀Co₂₀Cr₁₀V₄Al_x high-entropy alloys transforms from single-phase structure of face-centered cubic (FCC) to dual-phase structure of FCC and body-centered cubic (BCC). Also, the strength increases and ductility decreases. The Fe₃₄Ni₂₀Co₂₀Cr₁₀V₄Al₁₂ high-entropy alloy annealed at 900 ℃ exhibits an excellent strength-ductility balance, with yield strength, tensile strength and elongation to failure at 593 MPa, 1009 MPa and 32.13%, respectively. With Al content of 5%, the as-cast and annealed high-entropy alloys remain single FCC phase. However, with Al content of 8%, 12% and 15%, the high-entropy alloys all become FCC-BCC phase. The annealing treatment promotes the precipitation of BCC phase, and the proportion of BCC phase increases with increasing annealing temperature.