Molecular dynamics simulations are carried out to investigate the effect of the occupation of the cages on the stability of sI CO2 hydrates. Three types of cage occupations are concerned. The TIP4P/EPM2/DUAN potential models are used for the water-water, CO2-CO2, water-CO2 intermolecular interactions. The simulation results show that the occupation of the large cage is preferable compared to the occupation of the small cage. It may be induced that the hydration number of sI CO2 hydrates is mostly to be 9.