  In this paper, we reveal the branching structure for a non-homogeneous random
walk with bounded jumps. The ladder time $T_1,$ the first hitting time of
$[1,\infty)$ by the walk starting from $0,$ could be expressed in terms of a
non-homogeneous multitype branching process. As an application of the branching
structure,
  we prove a law of large numbers of random walk in random environment with
bounded jumps and specify the explicit invariant density for the Markov chain
of ``the environment viewed from the particle" .The invariant density and the
limit velocity could be expressed explicitly in terms of the environment.
