Based on the fact that high quality thermoelectric materials require the combined characteristics of “phonon glass with electronic crystal”, and according to the first principle calculation, a new method has thus been proposed for screening materials with the above characteristics in binary MXn semiconductor layered materials. Due to the weak van der Waals force between the layers, the lattice thermal conductivity in the out-of-plane direction is very low, making it a good “phonon glass” material, with the electron transport ability in the out-of-plane direction related to the M element and the atomic distance. With M being the main group element (e.g. SnSe), electrons are characterized with a good interlayer transport property due to the non-local pz orbital and the small interlayer distance (<4 ?). With M being a transition metal element (e.g. MoS2), the local d orbitals and the large cation-layer spacing (>6 ?) make it impossible for electrons to travel between layers. The thermoelectric properties of the layered material in the out of-plane direction can be judged by the size and type of the interlayer distance of the cation M (main group elementor transition metal), thus providing a theoretical guidance for screening potential high-ZT thermoelectric materials.