A combustion boundary of the Ti 44 Ni 47 Nb 9 alloy has been attained by combustion front quench (CFQ). The structures of the boundary and related products were analyzed using Xray and electronic probe scanning microanalysis (EPSM). It is found that an initial liquid phase mainly containing Ti 2 Ni phase is a precondition of combustion reaction and propagating combustion. The combustion propagation depends upon the infiltration of eutectic liquid, and the combustion synthesis is controlled by resolving components Nb and Ti into the eutectic liquid phase. It is confirmed that the reaction mechanism controlled by the components resolving, which is suggested by Vadchenko for bielement system, is suitable for SHS of TiNiNb.