The invention discloses a biomass gasification tar removing device and method based on chemical chain reforming. The device comprises a first cyclone separator, a preheater, a reforming reactor and an air combustion reactor which are sequentially connected, wherein the first cyclone separator is used for performing separation and dust removal on biomass gasification crude gas, the preheater is used for preheating the biomass gasification crude gas, the reforming reactor is used for subjecting the preheated biomass gasification crude gas and an oxygen carrier to a reforming reaction, the air combustion reactor is used for subjecting the oxygen carrier after the reforming reaction and air to a combustion reaction, a second cyclone separator for performing separation and dust removal on the oxidized oxygen carrier is connected between the reforming reactor and the air combustion reactor, and a third cyclone separator for performing separation and dust removal on the reacted gas is also connected with the reforming reactor. Tar macromolecules are partially oxidized into micromolecular substances such as CO, H2 and the like under the lattice oxygen and catalytic action of the oxygen carrier; the oxygen carrier is recycled between the reforming reactor and the combustion reactor, and regeneration of the oxygen carrier is simple.