Abstract: In order to investigate the difference of molten iron flow field in furnace hearth under normal erosion and adherent dross erosion,basing on the fluid mechanics two 3D mathematical models had been developed,which were used to describe the molten iron flow fields before/after hearth bottom erosion and the erosion of molten iron impacting on hearth bottom after slag forming.. And CFX software had been utilized to study the velocity of flow at bottom and streamlines at different locations. Before/after the occurrence of adherent dross circumfluence phenomena appeared around the hearth,and adherent dross have protective effect to a certain extent on hearth. The formation of adherent dross decreased the internal structure of the hearth and consequently accelerated the outflow of molten iron through taphole. It is suggested that under industrial production the adherent dross can be used to speed up tapping process and prolong the service life of blast furnace hearth via its protective effect on hearth.