Two-dimensional (2D) materials bring a great opportunity to fabricate molecular sieving membranes that can potentially break the permeability-selectivity trade-off. Although 2D laminar membranes with interlayer nanochannels as molecular sieving channel were widely studied, for most of reported 2D laminar membranes, it is of a great challenge to fabricate highly ordered interlayer nanochannels for mass transport. Herein, we report a novel kind of black phosphorene membrane which is made from the stacking of highly ordered 2D black phosphorene nanoflakes. The as prepared black phosphorene membrane shows H2 permeance > 1000 GPU and H2/CO2 selectivity > 100 for H2/CO2 mixed gas, demonstrating an extremely high gas separation performance. The DFT calculation results demonstrate that the interlayer galleries in the black phosphorene membrane allow the H2 passing through easily while block the other gases with bigger kinetic diameters, matching well with the experimental findings. The present results indicate that the interlayer galleries in the black phosphorene membrane can be applied as molecular sieving channels for gas separation.