The structure and property of Si2CN4(010) surface with different terminations were studied systemically by first principles calculation. The calculated cleavage energies of each possible surface showed that the Si—NⅡ bond located at the SiN layer was the strongest,while the Si—NⅠ bond connected with the carbodiimide was the weakest. As a result,the surface with the Si/NⅠ termination was the easiest to form. We have compared the atomic structure and electronic properties of un-optimized and optimized surface models. During the optimization of structure,the unsaturated surface atom,especially the NⅠ atoms at the surface would bond with each other to decrease the surface energies,since there are prominent density of states existing at the Fermi level of NⅠ atom. At the same time,the unsaturated C atoms do not have the tendency of bonding with each other,since their electronic state are more stable than NⅠ atom.