The invention provides an agent for reverse flotation of iron ore and a combination use method. The agent is composed of pH regulator sodium hydroxide, desorption agents, inhibitor causticity corn starch, activator calcium oxide and fatty acid collectors and is characterized in that the desorption agents are composed, by weight, of 40-42 parts of water glass, 4-6 parts of carboxymethyl cellulose and 7-9 parts of polycarboxylate. When the desorption agents are used, all raw material components are dissolved respectively according to the weight proportion and mixed, water is added, and therefore a desorption agent solution with the mass concentration of 0.04-0.06% is prepared. The desorption agents are applied to a reverse flotation process including one-time rough separation, one-time fine separation and three-time scavenging and a stage agent addition manner is adopted, so that the selective inhibition function on iron minerals by inhibitors in an original reverse flotation process is obviously enhanced, selectivity of the collectors is obviously enhanced, the tailing grade is reduced, the metal recovery rate is improved, fine-grain metal losses are reduced, emission reduction, yield increasing and efficiency increasing are achieved, the resource utilization rate is improved, and a new approach is provided for improvement of the micro-fine-particle iron ore reverse flotation technical index.