The invention discloses a method for preparing a two-dimensional layered material by stripping a ternary atomic crystal. The method comprises the following steps: dispersing a GaGeLi crystal as a precursor in ethanol, carrying out degassing with argon, then carrying out sealing with a Teflon adhesive tape, performing ultrasonic treatment, preventing a bathtub and liquid from overheating, keeping water cooling at 20-25 DEG C, and then carrying out centrifugal separation to obtain the two-dimensional layered semiconductor material 2D-GaGeLi. The optical band gap is related to the number of layers obtained by stripping, and the smaller the number of layers is, the larger the band gap is. The method has a great potential in photoelectric devices, photocatalysis and other aspects.