After volumetric fracturing of horizontal wells in tight reservoirs, the water in the fracturing fluid seeps into the reservoir and forms a "water invasion layers" in the near-well area, which affects the development effect of CO2 huff and puff. To clarify the influence of the water invasion layers on the effective range of CO2 huff and puff, the core physical simulation experiment method combined with low-field nuclear magnetic resonance imaging technology was adopted to analyze the remaining oil distribution characteristics and T2 spectra of different rounds of CO2 huff and puff, and to explore the influence of the water invasion layers and the coexistence of the water invasion layers and fractures on the effect of CO2 huff and puff and analyze its seepage mechanism. The research results show that in the area without fractures, the existence of the water invasion layers weakens the gravity override phenomenon of CO2 huff and puff, forms a smaller curvature arc-shaped huff and puff front, reduces the effective range and recovery degree of CO2 huff and puff; in the fracture area, the existence of the water invasion layers changes the huff and puff front from elliptical to "U" shape, and also reduces the effective range and recovery degree of CO2 huff and puff, but both are higher than those in the area without fractures; Water invasion layers affect the CO2 huff and puff effect and the range of action by hindering the contact between CO2 and crude oil and influencing the flow velocity distribution of CO2 in the seepage area. Whether in the unfractured area or the fractured area, when the water-invasion layer hinders the contact between CO2 and crude oil, CO2 always tends to break through the water-invasion layer at the location where the local pressure gradient is the largest, the flow velocity is the greatest, and the capillary resistance is overcome first. The research results clarify the distribution characteristics of remaining oil and seepage mechanism under CO2 huff and puff in tight reservoirs under the influence of water invasion layers, and also have certain reference significance for the development of similar oil reservoirs by CO2 huff and puff.