The invention provides a method of biomass grading pyrolysis gasification in a circulating fluidized bed comprising: feeding biomass into the lower-middle part of a carrying fluidized bed, mixing with high temperature synthesis gas and heat carrier from a turbulent fluidized bed, heating the biomass to carry out a pyrolysis reaction, and carrying the pyrolysis product upward; subjecting the cracked oil and gas to a gaseous phase catalytic cracking in an upper-middle part of the carrying fluidized bed, cracking the tar into methane, ethane and the like; subjecting the heat carrier, semi-coke and fuel gas after the reaction to the multi-stage of gas-solid separation, a large particle carrier and semi-coke following a first-level separation are used as the fuel gas cracking catalyst and the filter material for filtering and removing dust, and enter into a moving bed filter to separate out an ultra-fine ash and subsequently return to the turbulent fluidized bed so as to perform gasification reaction, the ultra-fine ash is delivered to the outside as a silicon-potash fertilizer product; the medium and small particle carrier and semi-coke separated from a second-level separation are directly recycled to the turbulent fluidized bed, the fine particles separated from a third-level separation is discharged to the outside as a silicon-potash fertilizer product, the moving bed filter further catalytically cracks a small amount of tar in the fuel gas into methane and ethane and removes the ultra-fine ash simultaneously, the purified fuel gas is delivered to the outside as a product.