In this paper, the crack problem of welded joint between NiTi SMA and Ti-6Al-4V was studied. The crack morphology and propagation state were analyzed, which was found that the microstructure uniformity of the fusion zone was poor. And there was a eutectic reaction layer at the fusion line of Ti-6Al-4V. A large number of brittle compounds NiTi2 phase led to severe hardening of the welded joint. By means of thermodynamic calculation and finite element simulation, the precipitation of brittle phase and stress distribution were studied, and the formation mechanism of crack defects was clarified. According to the above research, the beam offset welding process was used to melt the NiTi SMA with low melting point, which by the fusion brazing method to achieve the reliable connection. Optimizing the microstructure of the fusion zone and eliminating crack defects, the most suitable electron beam offset amount was 0.4 mm.