Samples of Ti-3Al-5V-5Mo alloy were compressed in both b and aqb phase region on a Gleeble 1500 Simulator. Compression tests were carried out in the temperature range of 700-1000℃ and strain rate range of 0.05–15 sy1. Experimental results show that the flow stress of Ti-3Al-5V-5Mo alloy decreases with the increase of temperature and the decrease of strain rate. At high strain rate, typically 5 and 15 sy1, discontinuous yielding followed by flow oscillations was observed in both b phase region and aqb phase region; at low strain rate, the flows display single peak stress. The flow stress at a strain of 0.2 was analyzed with a stand constitutive equation. Activation energy parameters were obtained, and they are 133.46kJymol for the b phase region and 661.90kJ/ymol for the α-β phase region. Microstructures of the compressed specimens in water-quenched conditions were critically observed. High temperature deformation mechanisms have been elucidated. In the b phase region, the operative deformation mechanisms are dynamic recovery at high strain rates and grain boundary sliding at low strain rates. In aqb phase region, the α phase undergoes dynamically recrystallization at both high and low stain rates.