The interfacial defects at the p-Si MBE layer/p-Si substrate interface have been observed and analysed. By solving Poisson equation, we can obtain the energy band diagram for this kind of structure with Shottky barrier at the surface and high dencity defects at the interface. The electron concentration at the defect level varying with external voltage can also be got by the calculation. Using deep level transient spectrascopy (DLTS) measurement to detect the interfacial defects, we found that the DLTS spectra for the emission and capture of electrons by the defect level can be got simultaneously at one temperature scan and the difference from conventional DLTS method is also discussed. The experimental results show that the energy level of the interface defects is located at Ec-0.30eV.