The microstructure evolution of Ti-55531 alloy with (β + global α) microstructure composition under 1K/min heating condition was observed by thermal expansion and SEM, and it was found that the microstructure evolution was α lamellae precipitate, dissolute and α globes dissolute. The kinetics equations of the growth / dissolution of the lamerllar precipitate and spherical precipitate were established. The simulation results showed that the growth and dissolution of lamellar α was affected by the Gibbs-Thomson effect, which reduced the stability of α lamella tips, thus resulting in the dissolution of α lamella tips at lower than the equilibrium temperature. The elongation of the α lamella tips follows the kinetics controlled by the mixed mechanism of bulk diffusion and interfacial diffusion, while the lateral thickening is controlled by bulk diffusion, and the bulk diffusion control dissolution of α lamella. global α growth at low temperature is controlled by the volume diffusion of stable elements with a lower diffusion rate, and the solubility at high temperature is controlled by the volume diffusion of Al with a higher diffusion rate.