The invention relates to a device for implementing the efficient purification of biomass gas in a furnace, which comprises a reacting furnace, the reacting furnace is provided with a reacting area, a purifying channel and a gas outlet, an outlet at the bottom of the reacting area is communicated with an inlet at the bottom of the purifying channel, the gas outlet is located at the top of the purifying channel, an atomized spray device is arranged in the purifying channel, and the spray direction of the atomized spray device and the gas flow direction of the purifying channel are opposite. According to the invention, the atomized spray device is integrated to the inside of the reacting furnace, atomized water sprayed from the atomized spray device is in contact with a high-temperature biomass gas contra-flow rising in the purifying channel, so that on the one hand, dust is adhered, thereby achieving the effect of dust removal; and on the other hand, tar is adsorbed, the tar and water mist are settled in high-temperature carbon residues to perform reforming reaction, and gas can be cooled, so that the quality of biomass gas is promoted to a certain extent so as to realize the stability and convenience of processing and application of back-end biomass gas. The invention also relates to a method for implementing the purification of biomass gas. The device and the method disclosed by the invention can be applied to the purification of biomass gas.