The supercritical water gasification of biomass technology is a promising approach for the efficient and clean conversion of wet-biomass to hydrogen-rich gas production. Many of the biomass materials are of rodlike shape and gasified in supercritical water fluidized bed. So the particle-fluid two-phase flow behaviors insider supercritical water fluidized bed are of great importance. Constrained by the extreme operating condition, numerical methods, such as the Euler-Euler method and Euler-Lagrange method, are used to study the flow behaviors inside the supercritical water fluidized bed. As the accuracy of these methods are depended on the drag force model and there is little investigation on that at supercritical condition, this work is focused on the drag coefficient of cylinder biomass particle with different ratio of length to diameter. The simulated results show that there is no differ- ence for the drag coefficient of a certain particle at different condition when the Reynolds number is same. The variation tendency of the pressure and viscous drag coefficient with Reynolds number and the ratio of length to diameter is also given in this paper.