Abstract: In this paper the effect of the carbonate foaming agents which are composed of dolomite, limestone and barium carbonate on the foaming of molten LF slag is discussed. In the laboratory the nine kinds of foaming agent are tested in the two kinds of molten slag. The foaming time and the foaming height of the molten slag are measured. The foaming index of the molten slag is calculated. The results show that the foaming agents of the single component have different foaming behavior because the decomposition temperatures of carbonate are different. The foaming index of the foaming agent composed of the three components (dolomite,limestone and barium carbonate),the mixture ratio of which is equal,is the largest in the nine kinds of foaming agent.