The diffusion bonding of TC21 titanium alloy with initial grain size of 2 μm was performed at 780-980 oC for 5-90 min. The microstructure, bonding quality, microhardness and deformation ratio of the joints were analyzed. It is found that the interface bonding ratio can achieve 100% and the deformation ratio can be controlled within 10% when diffusion bonding is performed at 880 oC for 15-30 min. The microhardness of the joints increases with increasing of bonding temperature, but it shows a peak value as the bonding time is prolonged. When the joint is bonded at 880-930 oC, fully equiaxed structures are observed, and with increasing of bonding temperature, the sizes of α and β phases are increased; but when bonding temperature is up to 980 ℃, fully lamellar structures are obtained. When the joint is bonded at 880 oC for 5-60 min, the size of α and β phases increases with prolonging of bonding time. However, when the bonding time is prolonged to 90 min, the sizes of α and β phases decrease slightly