The invention discloses a preparation method of a lanthanum-loaded modified bentonite dephosphorization material. The preparation method comprises the steps as follows: performing ultrasonic treatmenton a lanthanum chloride solution in an alkaline environment, mixing the treated solution with bentonite, then, performing stirring and ultrasonic treatment, and finally, performing cleaning, filtration, grinding and sieving to obtain the lanthanum-loaded modified bentonite dephosphorization material. Compared with the prior art, the method has the advantages that selected raw materials are sufficient, natural, non-toxic, convenient to use and low in cost, the treatment process is simple, the treatment cost is lower, used raw materials are environment-friendly materials, secondary pollution isavoided, and meanwhile, the preparation time is obviously shortened. The dephosphorization material prepared with the preparation method of the lanthanum-loaded modified bentonite dephosphorization material has the phosphorus removal rate up to 90% or above and has characteristics of high efficiency, controllability and the like.