The invention provides a system and method for activated carbon preparation tail gas coupled biomass direct-fired denitration. The system comprises a carbonization furnace, an activation furnace, a secondary combustion chamber and a biomass incinerator, wherein the carbonization furnace is used for performing a carbonization reaction on a raw material and generating a carbonized material and an initial high-temperature pyrolysis gas; the activation furnace is used for performing an activation reaction on the carbonized material and generating residual gasified gas; the secondary combustion chamber is used for receiving the initial high-temperature pyrolysis gas generated by the carbonization furnace through a first pipeline and receiving the residual gasified gas generated by the activation furnace through a second pipeline for combustion; and the biomass incinerator is used for receiving tail gas generated by the secondary combustion chamber and/or the carbonization furnace through atail gas pipeline so as to perform a denitration reaction. According to the system and the method provided by the invention, various unburnt tail gases generated in the carbonization and activation processes of activated carbon preparation are introduced into the biomass incinerator and react with nitrogen oxides generated by biomass incineration, so that the purpose of removing the nitrogen oxides is achieved, and meanwhile, the tail gases of activated carbon preparation can be efficiently and cleanly utilized.