The changing rules of flow stress at high temperatures for TC18 titanium alloy were studied by thermal simulation experiment, in temperature ranging from 750 to 950 ℃, at strain rate from 0.01 to 10 s-1 and the deformation degree of 60%. The constitutive equation of TC18 Ti alloy was derived through Arrhenius hyperbolic sine function. According to the experimental results, the processing maps of TC18 Ti alloy were developed for strain of 0.3 and 0.5. The results show that flow stress of TC18 titanium alloy decreases with the increase of deformation temperature and the decrease of strain rate. Under the experimental conditions, TC18 titanium alloy shows two kinds of softening mechanism of dynamic recovery and recrystallization. Arrhenius hyperbolic sine function can well describe the constitutive equation of the TC18 titanium alloy. The result of processing map shows that three unsteady zones of high temperature deformation appear on the process map at strain of 0.3. The two unsteady zones of high temperature deformation appear on the process map at strain of 0.5. From the processing maps, better thermal processing interval is in a temperature of 830 ~ 920 ℃ and at strain rate of 0.01~0.32 s-1 region