  For a $2n+1$-dimensional compact Sasakian manifold, if $n\ge 2$, we prove
that the analytic germ of the variety of representations of the fundamental
group at every semi-simple representation is quadratic. To prove this result,
we prove the almost-formality of de Rham complex of a Sasakian manifold with
values in a semi-simple flat vector bundle. By the almost-formality, we also
prove the vanishing theorem on the cup product of the cohomology of semi-simple
flat vector bundles over a compact Sasakian manifold.
