  Topological edge states at the boundary of quantum spin Hall (QSH) insulators
hold great promise for dissipationless electron transport. The device
application of topological edge states has several critical requirements for
the QSH insulator materials, e.g., large band gap, appropriate insulating
substrates, and multiple conducting channels. In this paper, based on
first-principle calculations, we show that Bi$_{4}$Br$_{4}$ is a suitable
candidate. Single-layer Bi$_{4}$Br$_{4}$ was demonstrated to be QSH insulator
with sizable gap recently. Here, we find that, in multilayer systems, both the
band gaps and low-energy electronic structures are only slightly affected by
the interlayer coupling. On the intrinsic insulating substrate of
Bi$_{4}$Br$_{4}$, the single-layer Bi$_{4}$Br$_{4}$ well preserves its
topological edge states. Moreover, at the boundary of multilayer
Bi$_{4}$Br$_{4}$, the topological edge states stemming from different
single-layers are weakly coupled, and can be fully decoupled via constructing a
stair-stepped edge. The decoupled topological edge states are well suitable for
multi-channel dissipationless transport.
