The disclosure relates to a method for characterizing a two-dimensional nanomaterial sample. The two-dimensional nanomaterial sample is placed in a vacuum chamber. An electron beam passes through the two-dimensional nanomaterial sample to form a diffraction electron beam and a transmission electron beam to form an image on an imaging device. An angle θ between the diffraction electron beam and the transmission electron is obtained. A lattice period d of the two-dimensional nanomaterial sample is calculated according to a formula d sin θ≅dθ=λ, where λ represents a wavelength of the electron beam.