A organic solvent free, new carboxylation pathway for C-H bond of terminal alkynes with supercritical CO2 (ScCO2) has been developed by using Ag(I)/DBU (1,8-diazabicyclo(5.4.0)undec-7-ene) catalytic system to obtain propiolic acid products with excellent yields in this work. In our reaction system, ScCO2 not only acts as reactive solvent but also as reactant. DBU plays the roles of co-catalyst, nucleophile and base, and obviously enhances the reaction rate in ScCO2. The Ag(I)/DBU catalytic system exhibits higher activity and wide substrate scope. Notably, both liquid and solid terminal alkynes can smoothly react with ScCO2 to produce desired product. The reaction pathway of functionalized propiolic acid formation from the carboxylation of terminal alkynes with CO2 is environment-friendly, simple, and economic.