The energy and electronic structure of several Mg-Ce intermetallic compounds with different structure types were investigated using the first-principle pseudopotential plane-wave method. Based on the calculations of formation heat of and cohesive energies, their structural stability was analyzed. The results show that the structure types with the strongest alloying ability and the highest structural stability are DO3, C15, Ba, C15 and DO3, respectively, for the Mg3Ce, Mg2Ce, MgCe, MgCe2, MgCe3 intermetallic compounds. After compared the DOS (density of state) of these phases with different structure types, the results show that the discrepancy in structural stability of Mg-Ce intermetallic compounds can be attributed to the difference in the bonding electron numbers at Feimi level, which mainly originates from the contribution of valence electrons of Mg(3s), Mg(2p), Ce(5d) and Ce(4f) orbits. The less the valence electrons at Feimi level, the better the structural stability of Mg-Ce intermetallic compounds.