The invention provides a preparation method and application of a rare earth ore flotation collecting agent and belongs to the technical field of ore flotation. The preparation method comprises the following steps of 1, mixing gutter oil, methyl alcohol and concentrated sulfuric acid according to the mass ratio, namely (1.0-1.2): (1.1-1.8): (0.05-0.09), of the gutter oil to the methyl alcohol to the concentrated sulfuric acid, and stirring the materials at the temperature of 60-90 DEG C to make the materials to react for 5-12 hours, so that a first product is obtained; 2, mixing hydroxylamine hydrochloride, water and sodium hydroxide according to the mass ratio, namely (1.0-1.3): (6.4-9.3): (1.9-2.4), of the hydroxylamine hydrochloride to the water to the sodium hydroxide, and stirring the materials at the temperature of 20-30 DEG C to make the materials to react for 1-3 hours, so that a second product is obtained; and 3, adding the first product to the second product according to the mass ratio, namely (1.0-1.2): (0.28-0.48), of the first product to the second product, and stirring the two types of products at the temperature of 40-60 DEG C to make the products to react for 4-6 hours, so that the collecting agent is obtained. By means of the rare earth ore efficient flotation collecting agent, the problems that existing floatation collecting agents are high in cost, poor in selectivity and difficult to operate in production, so that production technological processes are complex, and the rare earth concentrate grade and the index of the recovery rate are not ideal are solved.