Experiments for decomposition rate were carried out in subcritical and supercritical water in a batch-type reactor biomass set up by ourselves. Glucose was used as a model compound, and CaO was used as CO2 remover in experiments. The effects of temperature, pressure, residence time, initial concentration of glucose and n(Ca)/n(C) on glucose reactions were examined. The optimal process was also suggested after added CaO. Under the condition of 500°C, above critical pressure, 3-10 min resident time, n(Ca)/n(C) of 0.4-0.5.