  Using the single-mode approximation, we first calculate entanglement measures
such as negativity ($1-3$ and $1-1$ tangles) and von Neumann entropy for a
tetrapartite W-Class system in noninertial frame and then analyze the whole
entanglement measures, the residual $\pi_{4}$ and geometric $\Pi_{4}$ average
of tangles. Notice that the difference between $\pi_{4}$ and $\Pi_{4}$ is very
small or disappears with the increasing accelerated observers. The entanglement
properties are compared among the different cases from one accelerated observer
to four accelerated observers. The results show that there still exists
entanglement for the complete system even when acceleration $r$ tends to
infinity. The degree of entanglement is disappeared for the $1-1$ tangle case
when the acceleration $r > 0. 472473$. We reexamine the Unruh effect in
noninertial frames. It is shown that the entanglement system in which only one
qubit is accelerated is more robust than those entangled systems in which two
or three or four qubits are accelerated. It is also found that the von Neumann
entropy $S$ of the total system always increases with the increasing
accelerated observers, but the $S_{\kappa\xi}$ and $S_{\kappa\zeta\delta}$ with
two and three involved noninertial qubits first {\it increases} and then {\it
decreases} with the acceleration parameter $r$, but they are equal to constants
$1$ and $0. 811278$ respectively for zero involved noninertial qubit.
