In this paper, we study the formality of $K(\Gamma, 1)$. We prove that
$K(\Gamma, 1)$ is formal when $\Gamma$ is a semi-diret product of two
torsion-free finitely generated abelian groups or a lattice in a semi-direct
product of two abelian Lie groups given by a semi-simple action. Let $\Delta$
be a torsion-free finite extension group of such $\Gamma$. We prove that
$K(\Delta, 1) $ is also formal. In particular, $K(\Delta, 1)$ is formal when
$\Delta$ is torsion-free virtually abelian group.