Spontaneous Al2O3 reinforced TiAl composite was prepared by reaction synthesis with hot pressing. The effect of doping Nb2O5 on microstructure was investigated as well. Adopting DTA, XRD analysis, their reaction courses were analysed and discussed. SEM, XRD, metallography analysis and other test showed that it is niobium oxide improved aluminium thermal reaction and released much higher energy which made the composite could be sintered under lower temperature. Meanwhile, the doping of Nb2O5 has a function to control and alter the proportion of the matrix (TiAl: Ti3Al)phase, strengthen the forming of spontaneous alumina composition in the material, and produce greater influence on the microstructure.