NOVELTY - The method comprises executing a density variation separation of the fermented raw material under a function of rotationally flowing waterpower to make the material liquid in a status delaminated into a light phase, a moderate phase and a heavy phase, adding the raw material and a straw of the light phase flow into a separator (5) for primary cutting and crushing, and mixing the raw material under the condition of the rotationally flowing waterpower and then allowing the waterpower to the moderate phase of a stripping separator.    USE - The method is useful for pre-treating fermented raw material for large-scale biogas engineering, where the fermented raw material includes livestock, poultry manure, sludge, domestic organic waste, straw and weeds.    ADVANTAGE - The method is capable of simply, rapidly, economically and effectively pre-treating the fermented raw material with high stability and reliability in a convenient manner.    DETAILED DESCRIPTION - The method comprises executing a density variation separation of a fermented raw material under a function of rotationally flowing waterpower to make the material liquid in a status delaminated into a light phase, a moderate phase and a heavy phase, adding the raw material and a straw of the light phase flow into a separator (5) for primary cutting and crushing, mixing the raw material under the condition of the rotationally flowing waterpower and then allowing the waterpower to the moderate phase of a stripping separator, separating and removing the heavy phase material by a sand precipitating separator (4), conditioning the moderate phase liquid to the appropriate concentration and then passing to a material mixing crusher, completely crushing moderate and a short fiber material in the raw material, and pumping the fiber material into an anaerobic reactor through a unit material discharger. An INDEPENDENT CLAIM is included for a fermented raw material pre-treating device.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a fermented raw material pre-treating device.    Container (1)    Stripping mixer (2)    Circulating tank (3)    Sand precipitating separator (4)    Separator (5)    Suspended cutter. (6)