The invention discloses a biomass pyrolysis gasification method and a biomass pyrolysis gasification system. The method comprises the following steps: (1) mixing a dried biomass raw material and a microwave catalyst on a helical feeder, and pushing the materials into a microwave reactor for pyrolysis gasification after the material reaches 100 to 300 DEG C; (2) performing gas-solid separation on a pyrolysis product to obtain a gaseous pyrolysis volatile component and solids; (3) causing the solids to return to the reactor and enter a riser together with solids left in the reactor for combustion, and performing cyclone separation on a combustion product to obtain a regenerated catalyst and high-temperature flue gas; (4) performing high-temperature pyrolysis reaction on the regenerated catalyst and the gaseous pyrolysis volatile component obtained in step (2) to obtain a high-quality biomass gas product through a return pipe. The biomass pyrolysis gasification system comprises a raw material dryer, a microwave generator, a pyrolysis reaction cavity, a riser combustor and the return pipe. The method and the system are high in pyrolysis speed and low in energy consumption, obtained biomass gas is high in quality, and has broad application prospect, and the requirement of synthesis of a liquid fuel can be met.