Abstract: The hot workability of the 40%SiCp/Al composites (volume fraction) was studied by isothermal compression deformation on Glebble-1500D thermal simulated test machine at the deformation temperature of 350~500 ℃ under the strain rate of 0.01~10.00 s⁻¹. The thermal deformation of the composites was analyzed according to the true stress-strain curves, and the constitutive equation was established. The strain rate sensitivity index and power dissipation efficiency factor were calculated by dynamic material model, and the power dissipation diagram, instability diagram, and two-dimensional processing map were obtained. The results show that, the strain rate and deformation temperature significantly affect the flow stress. Under the same strain rate, the flow stress decreases with the increase of deformation temperature; at the same deformation temperature, the flow stress increases with the increase of strain rate. According to the processing map, the power dissipation efficiency factor is large under the condition of high temperature and high strain rate, illustrating the microstructure transformation in the deformation region. The strain has little effect on the instability region and processing region, and the power dissipation efficiency factor increases with the increase of strain. The recommended hot working conditions for the composite is as the deformation temperature of 436~491 ℃ and the strain rate of 0.04~9.97 s⁻¹.