The martensitic transformation of Ni-Ti shape memory alloy was investigated by X-ray diffraction analysis aided X-ray diffraction pattern simulation. Using the wire shape samples the X-ray diffraction patterns were measured at every 10°C from 0°C to 80°C. The software that simulated the X-ray diffraction patterns using by the data of already known lattice constants was developed on the basis of the Bragg's law and the intensity laws. First we confirmed that the X-ray pattern measured by arranging wire samples and attaching the sample holder coincided that of the powder method. Next the X-ray pattern at austenite phase (80°C) was compared with the simulated pattern of B2 crystal structure by the program and the state was identified as B2 structure. On the other hand at martensite phase (0°C) B2 and B19' structures were mixed in the crystal. Although the shape memory effect was expressed at this environmental temperature, it is considered that not only B19' structure but B2 structure is also related to the effect of shape memory effect.