Supercritical water gasification is suitable for gasifying biomass with high moisture content. Although biomass material can be easily decomposed in supercritical water, it can polymerize to form char products, which may result in serious problems such as plugging of the reactor. To depress char formation during gasification of biomass material in supercritical water. a combination of reactors was proposed in our previous study. In this study, we have improved the system by means of computational fluid dynamics (CFD) and verified it through experiments. With the improved reactor, 4.9 wt% glucose solution was successfully gasified at 673 K and 25.4 MPa; the carbon gasification efficiency was greater than 0.94.