Abstract: Gas hydrate were synthesized under the condition of 1 ℃ and 5 MPa by three types of gas compositions (CO₂-CH₄-N₂, the composition ratio was 70∶16∶14, 75∶11∶14 and 80∶6∶14), and the synthesized hydrate were measured by in situ Raman spectroscopy.The authors have had Raman spectrum for gas at the initial time of hydrate separation and hydrate at the end time of hydrate separation.The cavity occupancy and hydration index were calculated based on the object molecular various vibrational modes, and the Raman bands area ratio, combined with the model of “loose cage-tight cage” model and van der Waals-Platteeuw.The results show that the mixed-gas hydrates were both structure Ⅰ for the three gas samples, CO₂-CH₄ hydrates were synthesized by gas No.1 and No.2 gas sample, only CO₂ hydrate was synthesized by No.3 gas sample.The large cavity were occupied by CO₂ are 75.24%, 77.01% and 98.70% respectively.The large cavity were occupied by CH₄ are 22.20%, 22.64% and 0 respectively, the small cavity were occupied by CH₄ were 87.73%, 91.64% and 0 respectively.Hydration index of the three hydrates were 6.10, 5.89 and 7.77 respectively.