A b-oriented MFI zeolite membrane with variable thickness is provided. The MFI zeolite membrane is composed of zeolite crystals whose b-axes are all uniformly oriented perpendicular to a substrate. Further provided is a method for preparing the MFI zeolite membrane. The method comprises forming zeolite or zeotype molecular sieve seeds with different thicknesses on a substrate and adding the seeded substrate to a gel for the synthesis of an MFI zeolite containing a structure-directing agent to grow zeolite or zeotype molecular sieve crystals thereon. The MFI zeolite membrane overcomes the limitations of prior art zeolite membranes to maximize its applicability.