  Basing on the calculation of all the pairwise entanglement in the $n$ ($n
\leq 6$)-qubit Heisenberg XX open chain with system impurity, we find an
important result: pairwise entanglement can only be transferred through
entangled pair. The non-nearest pairwise entanglement will has the possibility
to exist as long as there has even number qubit in their middle. This point
means that we can get longer distance entanglement in solid system.
