  We consider a branching system of random walk in random environment (in
location) in $\mathbb{N}$. We will give the exact limit value of
$\frac{M_{n}}{n}$, where $M_{n}$ denotes the minimal position of branching
random walk at time $n$. A key step in the proof is to transfer our branching
random walks in random environment (in location) to branching random walks in
random environment (in time), by use of Bramson's "branching processes within a
branching process" .
