We performed first principle calculations based on density functional theory and GW approximation with Landauer approach to study ballistic electronic conductance and ballistic thermal conductance of black phosphorus (BP) whose dimensions are smaller than the mean free path of carriers. Ballistic electronic conductance of monolayer BP and bilayer BP with four different stacking styles, and ballistic thermal conductance of monolayer BP were investigated. The electronic transmission value along armchair direction is found to be a little higher than that along zigzag direction near the band gap energy range. Our calculations showed that, the Gamma point hole effective mass along zigzag direction is stacking style sensitive, while other Gamma point effective mass is independent of stacking style. We also reported the anisotropic ballistic thermal conductance of monolayer BP: the anisotropic ballistic thermal conductance ratio of zigzag-to-armchair approaches a constant (about 2.0) when the temperature is beyond 200 K. The reasons for these properties were discussed. (C) 2016 Elsevier B.V. All rights reserved.