The invention discloses a residue diluting agent for the desulfuration residue of molten iron for improving the floating performance of the desulfuration residue of molten iron which consists of the materials with the following weight percentages: 45 to 55 percent of fluorite powder, 22 to 28 percent of spodumene mine powder, 15 to 20 percent of industrial sodium carbonate, 3 to 5 percent of boraxand 2 to 4 percent of oxide scale powder; wherein, the content of CaF2 in the fluorite powder is equal to or more than 85 percent and the granularity is equal to or less than 0.178mm; the spodumene mine powder is manufactured by carrying out fine grinding on natural mines and the granularity is equal to or less than 0.150mm; the contents of the weight percentages of the main chemical components of the spodumene mine powder are as follows: 0.8 to 1.5 percent of Li2O, 71 to 76 percent of SiO2 and 18 to 20 percent of Al2O3; the oxide scale powder is manufactured by carrying out ball milling on arolling oxide scale and the granularity is equal to or less than0.178mm. In the industrial sodium carbonate, the content of Na2CO3 is equal to or more than 98 percent. The content of Na2B4O7.10H2O inthe borax is equal to or more than 95 percent. The residue diluting agent of the invention takes the fluorite powder, the spodumene mine powder and the industrial sodium carbonate as the main materials, can effectively improve the floating performance of the desulfuration residue of molten iron, is applicable for the fluxing of the desulfuration residue with large residue amount, high basicity, large viscosity and high melting point; besides, the costs of the materials are low.