Large numbers of experimental results show that carbides Me3C (Me means Fe, Ni, Co, Mn) are the primary carbon source to form diamond structure under the high temperature and high pressure (HPHT). In this paper, based on the empirical electron theory of solids and molecules (EET), the valence electron structure (VES) and interface structure factors of diamond and various carbides are calculated, and the boundary condition of electron movement in the improved Thomas- Fermi-Dirac theory by Cheng (TFDC) is applied to the carbide/diamond interfaces. It is found that the electron density of crystal plane in Me3C formed by C-C bonds is continuous with that in diamond at the first order of approximation. Compared with Ni-based carbides [Ni3C, (NiMn)3C)], the electron density difference of Fe-based carbides [Fe3C, (FeNi)3C, (FeMn)3C]/diamond interfaces is lower, and that of (FeNi)3C/diamond interface is minimum. The results show that the energy needed to transform carbon atomic groups into diamond structure is lower for Fe-based carbides than Ni-based carbides.