Spectral-domain optical coherence tomography (SD-OCT) system has the advantages of non-invasive, non-contact, fast imaging and low cost. It has important applications in the measurement of discrete interface of optical lens. However, the interference spectrum collected by spectral domain OCT system inevitably encounters some problems such as the unequal interval spectrum sampling and chromatic dispersion between two interference arms. In order to ensure that the axial resolution and sensitivity of the system are not reduced, subsequent data processing steps such as spectrum resampling and dispersion compensation need adding, which greatly reduces the real-time performance of measurement. In addition, in the actual measurement process, the required imaging area is often only a small part of the whole imaging area, the calculation of the whole imaging area brings a certain waste of computing power and resources. Moreover, in the positioning of discrete interface, the existence of sub-pixel deviation under limited axial resolution limits the measurement accuracy of interface. To solve the above problems, in this work proposed is a method of fast locating discrete interfaces based on complex master slave (CMS) OCT phase information. By combining the phase information of spectral domain and depth domain, the reconstruction template of CMS-OCT is solved accurately, and the phase information of CMS-OCT is used to achieve high-precision optical path difference detection and discrete interface location. Finally, experiments with precise optical gauge and discrete interface of optical lens verify that the proposed method can maintain high resolution and stability while fast locating is implemented.