The invention relates to a method for removing iron from a magnesium-containing sulfuric acid leaching liquid. The magnesium-containing sulfuric acid leaching liquid comprises 5-30 g/L of magnesium, 5-50 g/L of iron and other metals which mainly comprise copper, nickel and cobalt and have the concentration not higher than 10 g/L, wherein the concentration of H<+1> is 0.1-3.0mol/L. The method is characterized by comprising the following steps: adding an oxidant and oxidizing ferrous iron in the sulfuric acid leaching liquid into ferric iron; heating the leaching liquid to a temperature of 85-100 DEG C, fully stirring, in 2.5-7.0 hours, sequentially dropwise adding a 20-40wt% sodium salt solution and a MgO suspension in which the ratio of liquid to solid is (5:1)-(10:1) until the pH is 2.0-2.5 so as to remove iron, reacting and filtering to obtain iron-removal slag and an iron-removal leaching liquid; extracting copper from the iron-removal leaching liquid, precipitating nickel and cobalt with MgO, and concentrating and crystallizing magnesium salt to respectively recover copper, nickel, cobalt and magnesium. The method is low in cost, simple in process and operation, environmentally friendly and high in iron-removal efficiency.