By means of rapid water cooling to retain the microstructure state at high temperature, the phase transformation in TC6 titanium alloy during heating and cooling processes within the two phase field was investigated. The results show that with increasing the temperature during the heating process, the secondary α dissolves within a range of temperature between 700 and 850 °C but the primary α dissolves at 900 °C. The results of energy spectrum analysis show that Al element concentration in primary α is higher than that in secondary α, that is to say, primary α is more stable than secondary α at high temperature. During the cooling process, the primary α grows up preferentially at a higher temperature, while due to the formation of secondary α through nucleation and growth, it precipitates at a relatively lower temperature, and the secondary α precipitates can slow down the growth of the primary α. Furthermore, with reducing the holding temperature, the precipitation temperature of secondary α gradually decreases