The electronic structure and elastic properties of ground state spinel-CSi2N4 are investigated using pseudopotential plane-wave method with the general gradient approximation to the density functional theory. The geometric structures of spinel-CSi2N4 is firstly optimized to obtain the most stable state with the lowest energy and the lattice parameters, then the total energy, elastic constants, bulk modulus, band structure and density of states are calculated and analyzed, and finally, the hardness of the compounds are calculated and compared with spinel-C3N4.