In order to reveal the influence of mined-out areas formed by solid mining on replacement performance of gas hydrate CO₂ replacement mining， the comparative experimental study on CO₂/N₂ replacement mining of different gas hydrate saturations in mined-out area reservoirs and intact reservoirs was carried out. The results show that for the samples each with hydrate saturation of 30% and 45%， the CH₄ replacement rate of the mined-out area-reservoir is 5.5% and 9% higher than that of the intact reservoir， and the CO₂ storage per unit volume is increased by 26.5% and 39.8%， respectively. The existence of mined-out areas increases the molar ratio of the replacement medium to gas hydrate， thus providing a higher replacement driving force. Moreover， in the samples with high hydrate saturation， the mined-out area will also improve the diffusion of the replacement medium， resulting in the greater replacement effect of the reservoir containing mined-out area over the intact reservoir. Therefore， CO₂ replacement mining after solid mining can improve replacement mining efficiency， and contribute to carbon sequestration and formation stability. It is a potential safe and green mining mode for marine hydrate.