The reverse martensitic transformation of TiNi shape memory alloy fibers embedded in a pure aluminum matrix was studied in this paper. Results showed that the phase composition of the TiNi alloy fibers prior to prestraining at the room temperature had a significant influence on the differential scanning calorimetry (DSC) results of the composites. By a comparison to the high temperature X-ray diffraction (XRD) results, it was confirmed that the martensite was divided into two groups: the selfaccommodating martensite (SAM) and the preferentially oriented martensite (POM). The evolving process of the separation of martensite was discussed.