The invention provides a preparation method of a rare earth MCM-49 molecular sieve catalyst. The preparation method comprises the following steps: processing a Na-type rare earth MCM-49 molecular sieve containing a template agent in a mixed solution of cetyl trimethyl ammonium bromide (0.01 to 1.0 mol/L) and sodium hydroxide (0.01 to 2.0 mol/L) at a temperature of 20 to 100 DEG C for 10 to 150 minutes; drying the products, mixing the dried products with an binding agent (alumina) accounting for 10 to 40% of the total weight of the products and alumina, extruding the mixture into strips, burning the strips, carrying out exchange reactions in an oxalic acid solution, filtering, washing the strips with deionized water, drying the strips, and finally burning so as to obtain an H-type catalyst. The catalytic performance stability of the modified rare earth MCM-49 molecular sieve catalyst on alkylation reactions of benzene and butylene is prominently improved, compared to that of rare earth MCM-49 molecular sieve catalyst, which is unprocessed, or only processed by cetyl trimethyl ammonium bromide or sodium hydroxide.