To restrain the CO2 concentration in atmosphere, deployment of the carbon-negative energy generation devices is indispensable on account of the vast net carbon discharge every year. In this work, a novel and promising quadruple fluidized bed (QFB) reactor for the biomass/coal co-gasification is proposed to generate the high quality syngas whilst separate CO2 for further sequestration or utilization. To reveal the fundamental rules governing the reactor, a one dimensional model coupling the gas-solid flow hydrodynamics and the chemical reaction kinetics is built to simulate the physicochemical processes in the QFB, and the effects of several pivotal operation parameters on the reactor performance are comprehensively analyzed. It is found that the QFB runs stably under the given condition. The H-2 mole fraction in the dry syngas is higher than 70%, the CO2 mole fraction in the dry flue gas is around 97%, and the net carbon discharge can be negative when the biomass blending ratio is over 0.5. The methodology and findings in this work are of reference value for the lab, pilot or industrial scale QFB designation and operation, and can be extended to develop similar novel reactors for the carbon-negative energy generation.