Abstract: In the northern South China Sea, non-hydrocarbon gases such as CO₂ are abundant, which are both constructive and destructive for gas hydrates. When the natural gases containing CO₂ leak upward to shallow formations, CO₂ could be reduced to CH₄ as carbon source under appropriate conditions, forming gas hydrates within shallow sediments. The experiments of gas samples with different CO₂ and N₂ contents have indicated that the temperature for gas hydrate formation of CO₂-bearing gases is higher than that of CH₄-bearing gases, resulting in deeper occurrence of hydrates and bigger thickness of hydrate stale zones. If strong seepage happened, natural gases with higher CO₂ content would migrate upward to CH₄ hydrate zone through deep faults. The replacement process of CH₄ by CO₂ will start. The previous gas hydrates will be damaged or the saturation of CH₄ will decline.