The invention discloses a high-efficiency high-phosphorus molten iron dephosphorizing method used in the molten iron mixing process, and belongs to the technical field of pretreatment of molten iron. In the method, the process of mixing molten iron into an iron ladle by an iron mixing furnace/ vehicle is taken as the reaction time for dephosphorizing the molten iron in a melting pool; the potential energy of the molten iron is taken as melting pool stirring power; in a molten iron mixing impact area, a small granular solid oxidant and a small granular dephosphorizing agent with the same proportion as the iron output are continuously added; and in the whole molten iron mixing dynamic process, the silicon content of the molten iron, the slag basicity, the temperature and other dephosphorizing indexes are kept stable basically and the binary basicity CaO/SiO2 after slagging is controlled at 1.5-2.5. By the method, the molten iron dephosphorizing rate is higher than 75% and the rephosphorizing rate is lower than 3%; and the method has the characteristics of simpleness and convenience in operation, low process cost and the like.