To investigate the effect of solidification parameters on the solidification path and microstructure evolution of Ti-45Al-5Nb (at.%) aloy,Bridgman-type directional solidiifcation and thermodynamics calculations were performed on the aloy. The microstructures, micro-segregation and solidiifcation path were investigated. The results show that the β phase is the primary phase of the aloy at growth rates of 5-20 μm?s-1 under the temperature gradients of 15-20 K?mm-1, and the primary phase is transformed into an α phase at relatively higher growth rates (V >20 μm?s-1). The mainly S-segregation and β-segregation can be observed in Ti-45Al-5Nb aloy at a growth rate of 10 μm?s-1 under a temperature gradient of 15 K?mm-1. The increase of temperature gradient to 20 K?mm-1 can eliminate β-segregation, but has no obvious effect on S-segregation. The results also show that 5 at.% Nb addition can expand the β phase region, increase the melting point of the aloy and induce the solidiifcation path to become complicated. The equilibrium solidiifcation path of Ti-45Al-5Nb aloy can be described as , in which βR and γR mean the residual β andγ.