In this paper, the microstructures which were obtained through step-quenching and the mechanical properties of TC21titanium alloy were investigated systematically. The samples were solution treated at 900℃ for 0.5h, and then 9 sets of step-quenching experiments with temperature from 600℃ to 60℃ were carried out. The microstructure characteristics, hardness and tensile mechanical properties was measured and compared with different microstructures. The results show that the width of secondary α lath gradually decreased from 600℃ to 400℃, and nearly remained constant from 400℃ to 60℃. The variation of the macro-Vickers hardness is the same as that of β_trans matrix. The elongation and the reduction of area slowly increases with increasing the quenching temperature. The Vickers hardness, yield strength and tensile strength increase with decreasing the width of secondary α lath. The microstructure with a good combination of strength and ductility was obtained through the step-quenching at 300 to 400℃.