Abstract: The hot deformation behavior of 6111 aluminum alloy was investigated by high-temperature tensile testing on a Gleeble-1500 thermal-mechanical simulator at deformation temperatures of 350, 450, 550℃ and strain rate of 0.1, 1, 10 s^-1. It is shown that the flow stress of the aluminum alloy decreases when the temperature rises but increases when the strain rate increases, and the hot deformation behavior transfers from a strain-hardening deformation stage to a steady-state deformation stage. A unified viscoplastic constitutive model coupled with dislocation density was established in consideration of the effects of strain, temperature and strain rate on the flow stress. Material constants in the constitutive model were solved through a genetic algorithm. Predicted true stress-true strain curves calculated by this model are in good agreement with experimental data.