Abstract: Scanning electron microscope was used to observe γ′ phase in new non-magnetic roller steel X5NiCrTi2615MoAlVB which was treated by solid-solution at 1 000 ℃ and followed by aging 0-30 h at 660,710,760,810 ℃.And then, the softwares of Photoshop and Image-Pro Plus were used to calculate the average size of γ′ phase, and thus to study the kinetics of precipitate growth during aging process.The results show that after aging 0-30 h at 660-810 ℃, a lot of white and circular γ′ phases precipitated; With the increase of aging time, the size of γ′ phase increased gradually; In 0-2 h, γ′ phase grew up rapidly, and after that, the growth rate of γ′ phase gradually decreased; Under the same aging time condition, the higher the aging temperature, the larger the average size of γ′ phase. Fitted values of average size of γ′ phase were satisfied with the measured ones, the error between them was less than 10%.