By the liquid metal cooling method, the microstructure character of directional solidification of Ti-45Al-7Nb (at%) alloy was examined. The results show that both the solidification behavior and lamellar orientations are affected by withdrawing rate. The primary phase is α phase, and lamellar orientation is perpendicular to the growth direction at the withdrawing rate of 0.36 mm/min. The primary phase converts into β phase at the withdrawing rate of 1~10 mm/min, alloy solidify completely into the β phase field, and lamellar orientation tends to parallel or incline with the angle of 45° to the growth direction. When the withdrawing rate increases to 20 mm/min, the primary is also β-phase, followed by the peritectic reaction of L + β → α, and lamellar orientation is inclined with the angle of 45°~75° to the withdrawing direction