In order to find the influence of duplex aging on microstructure and mechanical properties of TC29 titanium alloy accompanied with primary α phase, different heat treatments and analysis methods including OM, SEM, and TEM were adopted. Results show that after treated by α+β two-phase solution and aging secondary α precipitates in TC29 titanium alloy are sub-micron level. After 895℃ solution and single aging, secondary α precipitates are mainly 100~300 nm in length. After 895℃ solution and duplex aging, "α clusters" are observed in β transformed microstructure and secondary α precipitates in them are thin slat-shaped. Compared with single aging, duplex aging results in an equal or lower microhardness. During the pre-aging treatment, a large amount of ω phases precipitate in β matrix, and the local element distribution gradually becomes inconsistent due to the diffusion near the primary α/β phase interface, where the “α cluster” is locally formed during the subsequent aging process.