Isothermal compression tests of 25vol% B₄Cp/2009Al composite have been carried out in the temperature range from 300℃ to 500℃ and the strain rate range from 0.001s_-1 to 1s_-1. The results show that high-temperature flow stress of the composite decreases with the increase of deformation temperature and the decrease of strain rate. The flow stress has been corrected by friction and the friction corrected stress is lower than experimental values. The influence of friction becomes more obvious with decreasing temperature and increasing strain rate. Then a constitutive equation considering the effect of stain on material constants (i.e. α, n, Q and A) is developed on the basis of Arrhenius type equation. Compared with the experimental results, the flow stress calculated by the constitutive equation possesses a high precision with the correlation coefficient of 0.992. Higher temperature and lower strain rate is beneficial for hot deformation of B₄Cp/2009Al composite.