The invention discloses a method for preparing low-phosphorus vanadium liquid by using wastewater subjected to vanadium precipitation, belongs to the field of metallurgy, and aims to solve the problems that the wastewater subjected to vanadium precipitation is difficult to treat and high in cost, broaden the treatment way of the wastewater subjected to vanadium precipitation and prepare qualified low-phosphorus vanadium liquid. In the method, the wastewater subjected to vanadium precipitation is taken as a leaching agent of vanadium-containing clinker, ammonium ions and phosphate ions which are contained in the wastewater react with magnesium ions to form a complex precipitate and remove most of phosphorus, calcium salt, aluminum salt or iron salt is added to deeply remove the phosphorus, and the solution is filtered to obtain the low-phosphorus vanadium liquid. By the novel method for preparing the low-phosphorus vanadium liquid, the wastewater subjected to vanadium precipitation can be recycled, the vanadium liquid with qualified phosphorus content can be obtained in the leaching process, the leaching and phosphorus removing processes are simplified, the wastewater discharge pressure of vanadium production enterprises is relieved, and raw materials are saved.