Abstract: To explore the characteristics of inorganic CO₂ flux (R_io) in coastal wetland soil and the inorganic absorption mechanism of CO₂ in soil, soils from three representative wetland types of mudflat, Suaeda salsa marsh, and Phragmites australis marsh in Jiaozhou Bay were collected. Based on the laboratory-controlled experiments, the characteristics of soil R_io were analyzed. The main influencing factors of R_io and their interactions were identified through the construction of a multifactor factorial model. In addition, the distribution of the absorbed CO₂ in wetland soil was clarified by isotope tracer technology. Results showed that the CO₂ absorption process existed in different types of soils in Jiaozhou Bay coastal wetland and the difference of R_io was significant, with the specific order of Phragmites australis marsh (average R_io of −0.171 mg/(kg·d)), Suaeda salsa marsh (average R_io of −0.230 mg/(kg·d)), mudflat (average R_io of −0.274 mg/(kg·d)). The soil R_io was negatively correlated with pH (r=0.82, p<0.05). Results of multifactor factorial model showed that the pH was the most significant influence for soil R_io in coastal wetland, and the interaction between pH and EC was the most intense. The ¹³C isotope tracer showed that the absorbed CO₂ was converted into soil dissolved inorganic carbon and soil inorganic carbon. In addition, within 1 - 24 h of the reaction, about 10% of dissolved inorganic carbon in the soil was converted to soil inorganic carbon, fixed directly into the soil in a solid form.