The invention provides a gasification device and a gasification method for preparing hydrogen-rich synthetic gas from biomass. The device comprises a biomass feeder, a mixer, a pyrolysis chamber, a gasification chamber, a gasified gas separator, a combustion chamber, a flue gas separator, a bin and a butterfly valve. In the method, the biomass gasifying process is divided into three parts, namelybiomass pyrolysis, semicoke gasification and heat carrier circulation. Through the method and the device, the synthetic gas with the tar content less than 200mg/Nm<3> and the H2/CO ratio more than 1.1 can be obtained, and the energy utilization rate and the process economy are obviously improved.