Abstract: Hot compression tests were conducted on TC4 titanium alloy at different temperatures in a range of 800-950℃ and at different strain rates in the range of 0.001-10s-1. Flow softening behavior of this alloy was investigated. The flow softening degree increased with increasing strain rate and decreasing temperature. Meanwhile, softening was mainly attributed to flow instability at temperatures of 800℃and 850℃, strain rates of 1 s?1 and 10 s?1. Conversly, softening was dominated by globularization of lamellar alpha at temperatures of 900℃and 950℃, strain rates of 0.001 s?1 , 0.01 s?1 and 0.1 s?1. In addition, the effect of strain was incorporated in the Arrhenius equation by considering the effects of strain on material constants including α、n、A and Q. The calculated flow stresses were compared with the experimental results. Results show that this model gives a precise estimate for the flow stress, especially at 800-850℃and 10s-1, 900-950℃ and 0.1s-1. The average deformation activation energy is about 403kJ/mol and the average strain rate sensitivity exponent of TC4 alloy is 0.26.