The critical karst zone is the central area with the combined action of the carbon cycle in the lithosphere, atmosphere, hydrosphere, and biosphere, and the interaction among different layers forms distinctive reaction systems, where CO₂ plays a vital role. Through monitoring the concentration of CO₂ in the overlying soil of Shuanghe cave, cave water, and atmosphere, the vertical conversion characteristics of CO₂ were systematically analyzed based on the carbonic acid equilibrium theory by adopting statistical analysis. The results show that the vertical conversion process of CO₂ is influenced by the changes in temperature inside and outside the cave, pH value of the dripping water and the process of degassing precipitation, and the source of CO₂ and ion saturation conditions, which are significantly different between the rainy and dry seasons. During the rainy season, the infiltration rate of atmospheric precipitation is high in the soil, forming a relatively stable enclosed environmental soil. The surface karst belt has weak activity in complementing CO₂ in the infiltration water, and the partial pressure of CO₂ (PCO₂) in the infiltration water varies in the range of 0.035~0.126 vol%, and the partial pressure of CO₂ in the water-atmosphere (△lg PCO₂) inside the cave is above 0. The cave water is featured by the corrosion property, and CO₂ in the lower part of the surface karst belt is the primary source of CO₂ in the cave water, whereas during the dry season, due to a small amount of precipitation, the infiltration water has sufficient time to receive CO₂ supplement from the soil and surface karst belt, forming an open system. The infiltration water changes in the range of 0.038~0.129 vol%, which is more conducive to the occurrence of the prior calcite precipitation (PCP). At this time, PCO₂ in the atmosphere inside the cave is smaller than that in cave water (△lg PCO₂ < 0), prompting the recurrence of degassing precipitation inside the cave. Also, both the soil and surface karst belt are the major sources of CO₂ in the cave water.