The invention discloses iron-based hot melting welding flux. The iron-based hot melting welding flux is composed of, by weight, 50-70% of iron oxide powder with 20-150 meshes, 15-30% of metal aluminum powder with 20-150 meshes, 0.5-5% of calcium fluoride powder with 40-150 meshes, 2-8% of iron alloy with 40-100 meshes, 10-25% of metal ion powder with 50-200 meshes and 0.1-2% of silicon dioxide powder with 40-100 meshes. The iron-based hot melting welding flux is low in cost, and the possibility of reactant splashing during welding is reduced; the welding effect is good, the corrosion resistance of the connecting position is good, and the electric conductivity is high; loosening and falling are not prone to occurring; an electrolytic bath is stable in operation, the current conveyance is uniform, and the pressure drop effect is obvious; and the maintaining cost and the potential safety hazard are reduced, application and popularization of non-electric welding materials are achieved, and the iron-based hot melting welding flux can be used for hot melting welding of cathode square steel of the electrolytic bath.