The invention relates to a method for recovering phosphorus in phosphate tailings with high magnesium content and preparing magnesium sulfate by adopting an indirect sulfuric acid method. The method comprises the following steps: 1) mixing the phosphate tailings with high magnesium content with a hydrochloric acid to react, so as to obtain one-time acidolysis filtrate and silicon slag, carrying out insulated suction filtration and washing to obtain a one-time washing solution; 2) carrying out secondary acidification on obtained one-time acidolysis filtrate and a one-time washing solution by using a sulfuric acid, so as to obtain secondary acidified filtrate and calcium sulfate sediments, aging, carrying out suction filtration and washing; (3) concentrating the obtained secondary acidified filtrate and the one-time washing solution once to obtain one-time concentrated filtrate and one-time concentrated solid, carrying out suction filtration and washing after cooling; 4) concentrating the obtained one-time concentrated filtrate and one-time washing solution for the second time, so as to obtain secondary concentrated filtrate and secondary concentrated solid, carrying out suction filtration and drying after cooling, so as to obtain a magnesium sulfate product; 5) returning the secondary concentrated filtrate to be mixed with the hydrochloric acid, leaching the phosphate tailings with high magnesium content in cycle, and extracting after certain concentration is achieved. The method is short in flow, convenient to operate, and high in recovery rate of magnesium.