The constitutive equation of Ti-6Al-3.5Mo titanium alloy had been researched with thermal simulation experiment. The experimental temperature was between 1030°C and 1120°C, and strain-rate was between 0.001 and 1.0, and the deformation degree was 50％. According to Arrhenius equation, a kind of constitutive equation of Ti-6Al-3.5Mo titanium alloy had been put forward. Compared the calculation results by constitutive equation with experiment results, the relative errors were less than 12%. For Ti-6Al-3.5Mo titanium alloy, strain-rate sensitivity coefficient being m=0.1688, and temperature sensitivity coefficient being s=10233.