A tar separator of a biomass gasifier comprises a housing communicated with a gas inlet pipe and a gas outlet pipe, wherein 1-5 dividing wall type heat exchangers are embedded in the housing; cooling water pipes of the dividing wall type heat exchangers are bent into a curved shape and fixed on a steel plate; a gas flowing space is remained between the dividing wall type heat exchangers and the housing; and a drawer type collecting tank for collecting condensed tar is arranged at the bottom of the housing. The cooling water pipes of the dividing wall type heat exchangers employed by the biomass gasifier are bent into the curved shape and fixed on the steel plate, and such a structure improves the cooling effect so that the tar can be separated better on one hand; on the other hand, the structure is capable of heating cold water in the water pipes by using heat in gasified biomass for combustion, thereby improving the thermal efficiency; and besides, the tar separator of the biomass gasifier is simple in structure, low in manufacture cost, easy to clean, easy to replace and better in practicability.