The invention discloses a composite slagging agent for a converter, which belongs to the technical field of slagging agents used in a converter steel-making process. The composite slagging agent comprises, by mass, 68 to 73 parts of calcium-free chromium slag, 12 to 15 parts of white corundum and 20 to 23 parts of limestone. The composite slagging agent for the converter provided by the invention does not contain CaF2, enables pollution to the atmosphere and the water resource by fluorine-containing gas and fluorinions to be avoided and integratedly utilizes waste calcium-free chromium slag which is difficult to recycle as a main raw material, so production cost for the slagging agent is substantially reduced, and elements like Cr and Fe in the calcium-free chromium slag are comprehensively utilized. According to the invention, formation time of the composite slagging agent is short and is reduced by about 30%, high production efficiency is realized, steel consumption is reduced by more than 3 Kg / t, consumption of slagging materials is reduced, and a substantial economic benefit is obtained.