The hot compression test of TA18 titanium alloy was carried out by Gleeble-3500 thermal simulation testing machine. The hot deformation behavior of TA18 titanium alloy was studied under the conditions of deformation temperature of 1073~1323 K and strain rate of 0.001~ 10 s-1. According to the obtained true stress-true strain curve, a modified nonlinear regression constitutive model of TA18 titanium alloy was established. The results show that the flow stress of TA18 titanium alloy is sensitive to strain rate and deformation temperature. The stress-strain curves show continuous dynamic softening characteristics in the dual-phase region, and the softening mechanism is mainly dynamic recrystallization. In the single-phase region, the characteristics of steady-state flow are presented, and the softening mechanism is mainly dynamic recovery. The hot deformation activation energy of TA18 titanium alloy in dual-phase region and single-phase region is 643.2 kJ/mol and 148.1 kJ/mol, respectively. The correlation coefficient R and the average absolute relative error AARE of the modified nonlinear regression constitutive model are 0.986 and 7.66%, respectively, indicating that the model can accurately predict the change of flow stress of TA18 titanium alloy. Additionally, with the increase of strain rate, the dynamic recrystallization degree of TA18 titanium alloy decreases first and then increases, and the dynamic recrystallization grain size decreases gradually. With the increase of temperature, the alloy undergoes isomerism transformation, and the alloy structure changes from equiaxed structure to basketweave structure.