The invention relates to a method for producing iron chloride, in particular to a method for producing iron chloride by using steel pickling waste liquor. By reacting the steel pickling waste liquor with sodium chlorate and hydrogen peroxide, and adding an appropriate amount of synergistic agent, the invention can not only recycle the steel pickling waste liquor for utilization and avoid polluting the environment due to improper disposal, but also decrease the production cost of the iron chloride and avoid the harm to the environment and the safety risk to the production operating environment due to using other methods for producing the iron chloride.