A model of "mixed phase flow" for preventing and cleaning fouling on inside tube wall by increasing three phase flow shearing stress was presented.The model can be used to study the mechanisms of preventing and cleaning fouling in the three phase circulating fluidized bed evaporator.The individual effects of operational parameters on three-phase flow shearing stress were studied.A saturated bittern solution was chosen as the work material.The fouling period of the saturated bitten could be prolonged effectively by increasing the amount of solid particles.