Abstract:The Ti-54wt% Ni shape memory alloy has been invest igated with a HVEM. It was found that the intense diffuse scattered streaks appeared in SADPs of B2-phase. In situ observation during heating showed that the streaks were related to the instability of the crystal lattice of B2-phase. SADPS taken form an area during tilting a specimen show that the diffuse scattered streaks are formed from the rel walls intersecting fundamental reciprocal points. SADPs of B2- Phase with the zone axises [012], [023], [011], [(?)33], [(?)33], [(?)11] and [(?)35] were taken. These SADPs show that the diffuse scattered streaks in SADPs usually lie in three different directions, intersect each other and form a network. Each streak consists of several sections. These sections lie in a line only in the [111] SADP. The sections are parallel each other, but do not lie in a line in other SADPs. Diffuse scattered streaks do not intersect the super-structure diffraction spots and centre spot, but the fundamental diffraction spots and can intersect each other at the positions without the diffraction spot. It can be assumed that the diffuse scattered streaks are formed by the rel walls lying on the {112}~* planes, intersecting at the fundamental points of the reciprocal lattice, and with certain dimensions. The rel walls can be used to explain the geometric characteristics of the diffuse scattered streaks and the change of angles between streaks in different SADPs. Finally, the formation and distribution of the rel walls as well as the length of diffuse scattered streaks in SADPs have also been discussed according to the diffuse scattering of electron by the transverse acoustic phonon waves with the wave vector lying on {112}~* planes in the lattice of B2-phase.