The invention relates to the field of comprehensive utilization of resources, and in particular relates to a comprehensive utilization method for iron and steel smelting dust washing wastewater. The method comprises the following steps: a) adding a precipitating agent and a flocculating agent into the iron and steel smelting dust washing wastewater to form a suspension; b) performing solid-liquid separation on the suspension, and collecting a solid phase and a liquid phase respectively; c) delivering the liquid phase to a reverse osmosis pre-enrichment system to complete pre-enrichment of alkali metals and chlorine ions and then obtain low salt water and a concentrated salt solution for washing smelting dust; and d) performing freeze drying on the concentrated salt solution to obtain a potassium salt and fresh water. The method realizes comprehensive utilization of the iron and steel smelting dust washing wastewater; the alkali metals and the chlorine ions can be pre-enriched through the reverse osmosis pre-enrichment system and freeze-dried, so that the energy consumption is reduced greatly compared with high salt water evaporation; meanwhile, the pre-enrichment manner has a relatively wide application prospect in the high salt wastewater treatment; the whole process is environment-friendly, economic and efficient.