Hot compression tests of Ti-5553 titanium alloy were conducted at deformation temperature of 800-860℃and strain rates of 0.1～10s-1.The relationship curve of work hardening rate θ and critical strain ε was obtained according to true stress—true strain curves. The critica1 conditions of dynamic recrvstallization of Ti-5553 alloy were studied with the inflection point criterion of curves. The critical condition of dynamic recrystallization was obtained using mode of Sellarsn.