<p>First principles calculation and Boltzmann transport theory have been combined to investigate the effect quantum size of the black arsenene on the electronic structure and thermoelectric properties. Calculations reveal the variation of phonon spectrums, band structure, and effective mass of the black arsenene with increasing the number of layers. It is also found that there is a transition from indirect to direct bandgap semiconductor for the black arsenene. Specially, the thermoelectric properties of the black arsenene are calculated with changing of experimental identification of critical condition and the maximum ZT_e of the black arsenene is found. The derived results could provide a new direction for the regulation of 2D thermoelectric properties of the black arsenene.</p>