<p>Based on first-principles density functional theory, the virtual crystal approximation (VCA) method was used to establish the FCC structural model and compute the structural properties of the high entropy alloys FeCoNiCuSi_x. Silicon (Si) was utilized to assess the structural properties, elastic properties, and thermodynamic stability of the alloy. Through iterative adjustments of simulation parameters, the optimal K-point mesh for the FeCoNiCuSi_x high entropy alloys is determined to be 7 × 7 × 7, with an energy cutoff of 650&#xa0;eV. The results indicate that with increase in Si content, the lattice constant of the alloy decreases, and the error between the initial lattice constant and the experimental value is within 2%, confirming the high reliability of the calculation. Concurrently, as the Si content increases, both bulk elastic modulus and shear elastic modulus exhibit similar trends. Specifically, when the Si content is 0.1 and 0.5, the both bulk and shear elastic moduli are significantly reduced, while under other Si content conditions, these modulus will increase. Additionally, the Poisson's ratio gradually decreases with increase in Si content, indicating a decrease in plastic deformation performance and an increase in brittleness of the material. Furthermore, thermodynamic stability declines with increase in Si content. Experimental results confirm that hardness increases with higher Si content. Computational predictions suggest the occurrence of a singularity point at a Si content of 0.1, whereas experimental observations reveal the singularity point at a Si content of 0.2. This discrepancy may be attributed to element segregation or uneven mixing during the smelting process, which causes a shift in the actual singularity point. Importantly, experimental results validate the simulation findings, confirming the consistency between the two approaches.</p>