Microstructure characterization and evolution analysis of Ti6242 alloy with equiaxed microstructure was studied by optical and scanning electronic microscopes, combining with image processing software. The origin alloy was processed under different heat treatments. Four parameters, including volume fraction Vα, size Dα, distribution density ρα and degree of aggregation Eα, were used to accurately describe the characteristics and evolution process of the equiaxed primary α phase. It was found that Vα, Dα, ρα and Eα all decrease with the solution temperature T increasing, and the relationships of Vα vs. T and ρα vs. T satisfy the linear and parabolic law, respectively. The declining rate of Vα increases with the T arising and decreases with time prolonging. With the Vα dropping, the content of element Al in β phase increases, while the content of Sn, Zr, and Mo decreases; the difference of the content of the four alloying element in β and α phase becomes smaller. At 850℃ and 800℃，the [Mo]eq of β phase is in the [Mo]eq range of α+β and metastable β alloy type respectively. After being quenched in water, the β phase occurs martensitic transformation at 850℃ and retains metastable β phase at 800℃。