The present invention discloses a Fe—Al-based metal membrane and preparation method thereof, which relate to the technical field concerning gas-solid separation under high-temperature, low-pressure working conditions, and mainly address the defects of conventional metal filter elements in the prior art such as high filtration resistance and low flux under low-pressure working environments. The preparation method of the present invention comprises the steps of: stirring and defoaming a mixture composed of a Fe—Al-based metal powder and an organic-additive-added water-based solvent, thus obtaining a cast slurry; casting a uniform membrane layer on a metal substrate layer having a required thickness on a casting machine, and performing drying treatment on it, thus obtaining a membrane green body; and, placing the dried membrane green body in a sintering furnace for degreasing, sintering, and alloy phase ordering treatments, respectively, thus obtain a prepared Fe—Al-based metal membrane.