The invention discloses a method for preparing ferric phosphate by utilizing a titanium dioxide by-product. The method comprises the following steps: preparing an extraction agent; adding the prepared extraction agent and a purified titanium dioxide by-product ferrous sulfate solution into sodium chloride and then mixing; extracting iron ions therein; adding ammonium dihydrogen phosphate and performing reverse extraction, thereby obtaining ferric sediment; heating and decomposing; and washing, drying and removing iron, thereby obtaining high-purity ferric phosphate. According to the method for preparing ferric phosphate by utilizing the titanium dioxide by-product, disclosed by the invention, the titanium dioxide by-product can be utilized to prepare the ferric phosphate, the obtained ferric phosphate is high in purity, the grain size is 0.45-0.5 micron, the grain size distribution is narrow, the cost is low, the specific surface area is less, the dispersity is high, the ratio of phosphorus to ion is at 1.0-1.01, and the wastewater output is less.