The invention relates to the preparing method of REY molecular sieve used for hydrocarbon kind fission and catalysis agent. It takes NAY molecular sieve with RE to the power 3 plus to carry on once ion interchange in water solution, and then bakes it for 1-3 hr. at 450-600 deg.C. in 100% flowing steam. As compare with the usual method which of through RE to the power3 plus interchange and air baking, the invented method not only simplifies the production processes, lowers the comsumption of rare earth and production cost, but also can reduce the rare earth comsumption which can be reverse interchanged and the concentration of Na to the power plus drops with great range as the prepared molecular sieve to carry on NH4 to the power plus interchange or water washing. After cleaning, it has the higher stability of water heating structure and higher fission active stability.