A method for preparing a molecular sieve SCR (selective catalytic reduction) catalyst and a prepared catalyst therethrough. In the method, several molecular sieves are mixed and modified by transition metal or rare-earth metal via ion exchange, then loaded Fe by equivalent-volume impregnation, and loaded Cu by one or more liquid ion exchange. This present invention, combined with several techniques, such as modification of stable molecular sieve by transition and rare-earth metal, Fe loading by equivalent-volume impregnation and Cu loading by one or more liquid ion exchange, and after through stable and effective modification and loading control, the obtained catalyst material is coated on a carrier substrate via size mixing and coating process to be prepared into an integral catalyst.