The invention discloses a continuous type preparation method of biomass activated carbon. The continuous type preparation method comprises the following steps of (1) activating, namely activating biomass raw materials by using phosphoric acid under the assistance of ultrasonic waves; (2) carrying out microwave heating carbonization at the microwave power of 500-800W for 3-10 minutes so as to obtain an activated carbon crude product, and meanwhile leading gas obtained after reaction into a gas absorber containing water; (3) purging and washing by using water vapor, condensing and drying, namely, purging and washing the activated carbon by using water vapor, then enabling the activated carbon to enter a condensation drier so as to be dried, thus obtaining an activated carbon finished product; and (4) recycling phosphoric acid, namely collecting an absorption liquid in the gas absorber and water vapor purging residual gas condensate in the step (3), namely recycling a phosphoric acid solution. The continuous type preparation method has the advantages of being simple in process, high in production efficiency, low in cost, economic and environment-friendly and can be used for preparing the activated carbon with excellent absorption performance, recovering the phosphoric acid at high efficiency so as to be recycled and realizing the industrial continuous type large-scale production.