High niobium (Nb) Ti-Al intermetallic compound composite coating was fabricated on BT3-1 titanium alloy surface by laser cladding process. According to differential thermal analysis (DTA) and thermogravimetry (TG) curves, the laser in situ synthesis reaction mechanism of Ti, Al, Nb three kinds of elements mixed powder under the argon and nitrogen protection was discussed. The phase composition and microstructure of composite cladding coatings were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show the composite coating is mainly composed of Nb elemental and γ-TiAl intermetallic compounds, α₂-Ti₃Al and Ti₃Al₂, and Nb is only part of the in situ reaction happened in coating. N₂ can reduce the reaction temperature and increase the reaction rate between Ti and Al, and also can promote the reaction between Ti and Al. The laser cladding composite coating does not appear columnar crystal having a laser cladding epitaxial growth characteristics, but produce the fine equiaxed grain structure.