  We show that the kernel of the Rumin Laplacian agrees with that of the
Hodge-de Rham Laplacian on compact Sasakian manifolds. As a corollary, we
obtain another proof of primitiveness of harmonic forms. Moreover, the space of
harmonic forms coincides with the sub-Riemann limit of Hodge-de Rham Laplacian
when its limit converges. Finally, we express the analytic torsion function
associated with the Rumin complex in terms of the Reeb vector field.
