High-entropy alloys with coexisting BCC and FCC structures usually have excellent comprehensive mechanical properties, and Al element can promote the transformation of Cu-containing high-entropy alloys from FCC to BCC structures to obtain the coexisting BCC and FCC structures. In order to illustrate the process of phase separation of high entropy alloys, a low cost Al-TM transition group element high entropy alloy is selected in this paper. Based on the Chan-Hilliard equation and Allen-Cahn equation, a three-dimensional phase field model of Al<sub>x</sub>CuMnNiFe high-entropy alloy is established and the microscopic evolution of the nano-Cu-rich phase of Al<sub>x</sub>CuMnNiFe high-entropy alloy (x = 0.4, 0.5, 0.6, 0.7) at 823 K isothermal aging is simulated. The results show that the Al<sub>x</sub>CuMnNiFe high-entropy alloy generates two complex core-shell structures upon aging: Cu-rich core/B2<sub>s</sub> shell and B2<sub>c</sub> core/FeMn shell, and it is found that the formed B2<sub>c</sub> plays an inhibitory role in the formation of the nano-Cu-rich phase through discussion and analysis, and this inhibitory role becomes larger with the increase of Al elements; the empirical formula is combined to make the Al<sub>x</sub>CuMnNiFe high-entropy alloy The yield strength of the Cu-rich phase changes with the aging time, and the overall yield strength of the high-entropy alloy has a trend of rising and then falling with the change of time, and the aging time of the peak yield strength and the alloy system are obtained according to the change of the curve, so that the best alloy system and aging time of the high-entropy alloy can provide reference for aging process.