Abstract: This article gives an overview of some recent advances in our research of hydrothermal conversion of biomasses，including mainly the production of low molecular weight carboxylic acids，such as acetic acid，lactic acid and formic acid from carbohydrate，lignocellulosic and cellulose biomasses，as well as glycerin，the by-product from bio-diesel fuel manufacturing process. Some mechanism of the hydrothermal conversion and the mutual effects of natural carbohydrate biomasses in hydrothermal reactions are also discussed. Additionally，the development of acetic acid production from plant-biomass via a pilot-scale continuous hydrothermal reaction system is presented.