With the rapid development of social economy, the problem of energy shortage is becoming more and more prominent in the world. At present, the development and utilization of renewable energy has been listed as the priority area of energy development in China. Algae plants contain abundant biomass energy, and have advantages such as high photosynthetic efficiency, strong carbon fixation capacity, fast growth rate, and wide distribution of sources, which is recognized as the development direction of sustainable green and clean energy. Glycine is an important derivative product in the process of algal hydrothermal liquefaction. The thermomechanical properties of glycine during liquefaction are the basic elements to understand and optimize the technology of algal hydrothermal liquefaction. The study of glycine hydrothermal liquefaction process can lay a foundation for the analysis of complex biomass hydrothermal liquefaction reaction. In this study, based on the high temperature and high pressure visible reactor of fused silicon capillary reactor (FSCR), combined with Linkam FTIR600 temperature control platform and Andor laser Raman spectrometer, the liquefaction process of glycine aqueous solution at 270~290 ℃ (pressures approximate to the saturated vapor pressure of water at ambient temperatures) was studied in situ by Raman spectroscopy. The effects of temperature and reaction time on the thermal decomposition of functional groups of glycine solution were analyzed by observing the relative Raman intensity changes of C—C stretching vibration peak (897 cm^-1), C—N stretching vibration peak (1 031 cm^-1) and C—O—O antisymmetric peak (1 413 cm^-1) during liquefaction. The activation energy, 357 kJ·mol^-1, and reaction rate constant k at different temperatures were obtained by using Avrami kinetic model. The thermodynamic properties of glycine liquefaction process were quantitatively determined. It is found that within the same liquefaction reaction time (10 min), when the temperature is lower than 290 ℃, the ν(C—C), ν(C—N), ν_as(COO^-) characteristic peak of glycine aqueous solution can be observed in the reaction chamber after cooling, but not when the temperature is higher than 290 ℃, indicating that the complete liquefaction temperature of glycine is about 290 ℃. The present study, based on the high-temperature and high-pressure visualization technology combined with in-situ Raman spectroscopy analyses, reveals the variation of the Raman peak intensities of characteristic functional groups of glycine at different temperatures during the hydrothermal liquefaction and provides deep insights into the pathway of hydrothermal liquefaction of algae. It is of great scientific and practical significance to understand the mechanism of algal hydrothermal liquefaction and promote the development and utilization of biomass energy.