  We study numerically the charge conductance distributions of disordered
quantum spin-Hall (QSH) systems using a quantum network model. We have found
that the conductance distribution at the metal-QSH insulator transition is
clearly different from that at the metal-ordinary insulator transition. Thus
the critical conductance distribution is sensitive not only to the boundary
condition but also to the presence of edge states in the adjacent insulating
phase. We have also calculated the point-contact conductance. Even when the
two-terminal conductance is approximately quantized, we find large fluctuations
in the point-contact conductance. Furthermore, we have found a semi-circular
relation between the average of the point-contact conductance and its
fluctuation.
