The addition of Ni as filler is one of the methods to restrain the crack of TiNi / stainless steel dissimilar material laser welding joint and realize its good connection, but the difference between filler metal Ni and base metal TiNi alloy will form the interface area, the welding heat input has a great influence on the microstructure and morphology of the interface area, which will affect the mechanical behavior of the whole joint. In this paper, TiNi alloy / Ni / 321 stainless steel laser welding joint with thickness of 0.2mm was obtained by using Ni as filler material in laser micro - welding. the effect of laser pulse width on the TiNi side interface of the welding joint was studied. The results show that, the interface zone of TiNi alloy side under different pulse width is composed of TiNi eutectic layer and TiNi3 intermetallic layer with different width.With the increase of pulse width, the average width of TiNi eutectic layer gradually decreases, the average width of TiNi3 intermetallic compound layer increases gradually, and the microhardness of interface zone increases with the increase of pulse width. The change of the melting amount of TiNi and the flow of Marangoni is the main reason that affects the width and microhardness of the interface zone.