A lattice Boltzmann model of gas flow in tree-shaped microchannel network is developed and numerically analyzed to investigate the behaviors of gas flow and boundary velocity slip in tree-shaped hierarchical network. The rarefaction effect, multiscale effect and bifurcation effect are all examined and analyzed. The velocity and pressure distributions, Poiseuille number and effective slip length in hierarchical networks are presented. The results indicate that the gas flow behavior in tree-shaped microchannel network is dependent on the rarefaction effect, multiscale effect and bifurcation effect. The boundary slip velocity along the streamwise decreases in a stepwise fashion, but the velocity slip degree owing to rarefaction effect intensifies with increasing branching level. The abrupt rise and fall of slip velocity as well as slight pressure recovery is observed at the bifurcations. In multi-scale tree-shaped hierarchical network, increases in branching level lead to larger Knudsen number, which induce larger effective slip length and smaller Poiseuille number. In addition, the gas rarefaction effects are enhanced when the width exponent of tree-shaped microchannel tends to be smaller in the hierarchical network. (C) 2014 Elsevier Ltd. All rights reserved.