The TiO2(B)/anatase dual-phase nanofiber exhibits enhanced photocatalytic activity when interfaces form during phase transformation of TiO2. To precisely control the formation of coherent interfaces between TiO2(B) and anatase, a thorough knowledge of phase transformation particularly from TiO2(B) to anatase (TA) is required. In our study, a crystallographic model in conjunction with transmission electron microscopy (TEM) was employed to investigate the phase transformation. The coherent interface with a crystallographic orientation relationship of TB//TA, (200)TB//(002)TA, and (020)TB//(020)TA predicted by the crystallography model was also observed by TEM experimentally. In addition, two types of incoherent interfaces that may deteriorate photocatalytic activity were examined and can be eliminated via an accurate tuning of calcination. The fundamental knowledge acquired from this work, therefore, provides a new insight to synthesize more efficient dual-phase TiO2 photocatalysts.