Supercritical water gasification technology has bright prospects because it can convert biomass into hydrogen-rich gaseous products in an effective and clean way. The devolatilization process is relatively fast, and char conversion is the rate-determining step in the whole gasification process. To discuss the kinetic model of char gasification in supercritical water, the quartz tube reactor was adopted as the reactor to omit the undesired catalytic effect of the reactor wall and bamboo charcoal was selected as typical char as a result of the low volatile content. The experiments were investigated within the operating range of temperatures of 700-900 degrees C and residence times of 5-20 mm. The experimental results were analyzed within the framework of homogeneous, non-reacted core, and random pore models. Dependences of the carbon gasification rate, residence time, and temperature were described in an assumption of the first-order reaction and the Arrhenius dependence. The calculation results showed that the random pore model fit the char gasification process in supercritical water best and the activation energy was 125.43 kJ/mol.