One of the high-temperature CO₂ sorbents lithium orthosilicates (Li₄SiO₄) was synthesized by using sol-gel method. The structures and the adsorption properties of Li₄SiO₄ were investigated by XRD, temperature-programming tests, and isothermal tests. In-situ FTIR tests were carried out to analyze the adsorption species and procedure. The results show that high purity (more than 90%) monoclinic Li₄SiO₄ could be obtained by adding citric acid into the LiNO₃-TEOs-Ethanol co-hydrolysis system. Such a Li₄SiO₄ material shows good CO₂ adsorption performance in the atmosphere of 2% CO₂ in He within the temperature range of 450-500℃. The major adsorption species on the surfaces of the samples are bicarbonates at lower adsorption temperature, and are ion-type carbonates and horizontal-type carbonates at higher temperature.