The invention relates to a method for processing biomass, which effectively solves the problems of the pyrolysis of biomass and the separation of products, the secondary processing of pyrolysis wood tar and the source of pyrolysis heat; the method comprises the following steps: the biomass enters a pyrolysis reactor after dried and milled, and forms charcoal and oil gas products through pyrolysis and carbonization; from a gas outlet of the lower part, a part of the charcoal enters a gasifier to react with air and generate carbon monoxide, and the other part enters a charcoal storage tank used for secondary processing; the oil gas with carbon dust sequentially passes through a settling chamber, a cyclone separator and a wire gauze filter to be separated from the carbon dust and then enters a fractionating tower for fractionation, thus obtaining intermediate heating value gas, pyroligneous liquid and wood tar, wherein, the intermediate heating value gas is mixed with the carbon monoxide in the gasifier and then the mixed gas returns and enters the pyrolysis reactor as the fuel of the reactor, the pyroligneous liquid enters a pyroligneous liquid storage tank used for secondary processing, and the wood tar enters a hydrogenation reactor to be hydrotreated with hydrogen catalyst and generate hydrogenation products through hydrogenation reaction. The method of the invention has simple process, and is environment-friendly and energy-saving.