The structure, stability and occupancy of methane hydrates were studied by the method of ab initio molecular dynamics simulation combined with quantum chemistry calculation. The optimum occupancy for five clathrate cages (5(12), 4(3)5(6)6(3), 5(12)6(2), 5(12)6(4) and 5(12)6(8), j is one, one, one, two, and five methane molecules, respectively, suggesting thatjust 5(12)6(4) and 5(12)6(8) cages are likely to form the multiply occupied methane hydrates. Moreover, our results show that the methane molecules in the large cage aggregate to form a cluster, which would be helpful to understand the formation of multiply occupied hydrates. (C) 2015 Elsevier B.V. All rights reserved.