The invention relates to a method for treating metallurgical off-gas acid-making waste water and belongs to the method for treating waste water. The method comprises the following steps of: pre-treating industrial waste barium residue; analyzing and measuring the pH value and the content of positive ions such as heavy metals and negative ions such as sulfate radical of the metallurgical off-gas acid-making waste water; adding an appropriate amount of industrial waste barium residue into the metallurgical off-gas acid-making waste water and stirring the mixture; and performing solid-liquid separation and the like. Detailed steps of the method are shown in the specifications. The method has the advantages of simpleness, practicability, high reaction speed, low cost, treatment of wastes with processes of wastes against one another, comprehensive utilization, easy solid-liquid separation, capability of laying a good foundation for the treatment and recycling of the waste water in the smelting industry and the like.