Large-size and high-quality single crystal diamond synthesized by microwave plasma chemical vapor deposition (MPCVD) have excellent physical and chemical properties, which makes them have great application prospects in jewelry, electronics, nuclear and ray detection and other industry fields. During CVD single crystal diamond growth, it is found that there is an obvious interface between the substrate and the epitaxial layer, as well as between the multiple growth layers which stop-continue to grow. The interface region was analyzed by polarization microscope, Raman spectra and photoluminescence spectra(PL). The bright image under polarization microscope and higher content of NV color centers compared with substrate and its epitaxial layers indicate that the interface area has high defect and impurity content. The results show that some measures should be taken to control the quality of high-quality single crystal diamond at the initial stage, and the preparation should be completed in one growth cycle as far as possible.