The water-insoluble lignin (WIL), water-soluble lignin (WSL) and kraft black liquor (KBL) were performed on a thermogravimetry coupled with Fourier transform infrared spectrometry (TG—FTIR) to study the impact of sodium cation on lignin CO2 gasification, respectively. The TG profiles of the WSL and KBL were analogical during the whole reaction owing to the presence of sodium cation. The WIL and WSL had similar chemical structure, but there were different reactivity of CO2 gasification. Sodium cation on lignin structure had a control effect on the formation of CO in the CO2 gasification of WSL.