Abstract: According to the theory of heat transfer, BF hearth bottom models were built based on actual examples by software with VC language, the calculated results in good accordance with the data of BF thermal couples. Temperature distribution and the capability of resistance to erosion were analyzed for the two prevalent kinds of hearth bottom, called "heat transfer method" hearth with small carbon bricks of high thermal conductivity and "heat isolation method" ceramic synthetic hearth bottom. Different ways in protecting hearth bottom were clarified by analyzing some actual examples. The result shows that the existence of a "protecting skull" with low thermal conductivity between hot metal and brick layers is the same essence of prolonging the life of hearth bottom, and the disadvantages of the two kinds of hearth bottom were analyzed.