The invention relates to a preparation method of a catalyst for removing trace amounts of alkenes in reformate. The invention is characterized in that the catalyst comprises the following components in mass percent: (1) 60-90% of molecular sieve, (2) 2.0-10.0% of rare earth oxide, (3) 0.5-4.0% of alkaline earth oxide, (4) 1.0-6.0% of phosphoric anhydride and (5) balance of aluminum oxide. The preparation method comprises the following steps: (1) mixing the molecular sieve and deionized water, pulping, sequentially adding rare earth salts and phosphates, filtering, drying, evenly mixing with aluminum oxide, adding a dilute nitric acid solution for strip extrusion or ball molding, drying, and roasting in the air atmosphere to obtain a molecular sieve loaded with rare earth and phosphorus; (2) while stirring the salt solution of Mg or Ca at high speed, adding a surfactant to obtain a highly dispersed Mg or Ca solution; and (3) immersing the molecular sieve with the same volume obtained in the step (1) into the solution obtained in the step (2), drying the product, and roasting in the air atmosphere to obtain a finished catalyst product.