After volumetric fracturing of horizontal wells in tight reservoirs，water from the fracturing fluid seeps into the reservoir and forms a “ water invasion layer ” in the near-well area，which affects the development effect of CO₂ huff- n -puff. To clarify the influence of the water invasion layer on the swept range of CO₂ huff- n -puff，core physical simulation combined with low-field nuclear magnetic resonance imaging was adopted to analyze the remaining oil distribution characteristics and T₂ spectra of CO₂ huff- n -puff at different cycles. The effect of water invasion layer，as well as the coexistence of water invasion layer and fractures on CO₂ huff- n -puff performance was investigated，and the corresponding seepage mechanism was analyzed. The results showed that in non-fractured zones，the existence of water invasion layer weakened the gravity override of CO₂ huff- n -puff，formed an arc-shaped huff- n -puff front with smaller curvature，and reduced the swept range and recovery degree of CO₂ huff- n -puff. In fractured zones，the water invasion layer changed the huff- n -puff front from elliptical to "U" shape，and also reduced the swept range and recovery degree of CO₂ huff- n -puff，but both indicators were higher than those in non-fractured zones. The water invasion layer affected the performance and swept range of CO₂ huff- n -puff by hindering the contact between CO₂ and crude oil and changing the flow velocity distribution of CO₂ in the seepage area. Regardless of whether fractures existed or not，when the water invasion layer hindered the contact between CO₂ and crude oil，CO₂ always tended to break through the water invasion layer at the position with the largest local pressure gradient，the highest flow velocity，where capillary resistance was overcome first. The research results clarified the remaining oil distribution characteristics and seepage mechanism of CO₂ huff- n -puff in tight reservoirs under the influence of water invasion layer，which provided certain reference for CO₂ huff- n -puff development in similar reservoirs.