The microstructural evolution and deformation micromechanism of cold-deformed TiNi based alloys, both in the martensite and parent phase conditions, have been reviewed in the present paper. The emphasis is placed on the modification of the microstructure proceed through atomic migration such as the coalescence and rearrangement of martensite variants and the adjustment and development of internal twinnings. The atomic configuration at the preexisting twinning boundaries after deformation have been revealed. The corresponding deformation micromechanisms were discussed.