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Hydrate-based carbon dioxide (CO₂) separation and capture is a new technology for achieving CO₂ emission reduction. However, it is still not commercially applied for the ambiguity of microscopic hydrate formation mechanism. In a constant volume experiment of hydrate formation, there are two or more pressure platforms, indicating that there might be two or more different hydrates formation in succession. In order to reveal the relationship between the microscopic process and the gas consumption in the process of hydrate formation, hydrate composition and formation mechanism of cyclopentane-CO₂ (CP-CO₂) system was investigated using a differential scanning calorimeter (DSC) and Raman spectroscopy. The results indicated CO₂-CP binary hydrate and CO₂ hydrate are formed successively, and they coexist in the final hydrate. CP-CO₂ binary hydrates forms preferentially, and as crystal seeds, inducing the formation of CO₂ hydrates. The two hydrates formation processes cause the two pressure-drops. The results provide a scientific basis for increasing the gas consumption in different stages of gas hydrate formation in the presence of hydrate formation promoter.