Isothermal-compression tests of B₄C_p/6063Al composites containing 20 vol.% B₄C were performed using a Gleeble-3500 device, at strain rates ranging from 0.001 s⁻¹ to 1 s⁻¹ and deformation temperatures ranging from 723 K to 823 K. The results showed that the high-temperature flow stress of B₄C_p/6063Al composites increases with the decrease in deformation temperature or the increase in the strain rate. After friction correction, the friction corrected stress was less than the original experimental stress. At the initial stage of deformation, the difference between the rheological stress after friction correction and the measured rheological stress is small, but with the continuous increase in the strain, the difference between the rheological stress after friction correction and the measured rheological stress is grows. Under the same strain, the difference between the rheological stress before and after friction correction becomes more significant with the decrease in the deformation temperature and the increase in the strain rate. Next, the material constants (i.e., α, β, Q, A, n) of B₄C_p/6063Al composites were calibrated based on the experimental data, and a constitutive equation was established based on Arrhenius theory. The experimental values and predicted values of the stress–strain curves are in good agreement with the stress–strain curves of the finite element simulation, and the validity of the constitutive equation was verified.