  In this paper, we introduce a concept of super-pseudoconvex domain. We prove
that the solution of the Feffereman equation on a smoothly bounded strictly
pseudoconvex domain $D$ in $\CC^n$ is plurisubharmonic if and only if $D$ is
super-pseudoconvex. As an application, we give a lower bound estimate the
bottom of the spectrum of Laplace-Beltrami operators when $D$ is
super-pseudoconvex by using the result of Li and Wang \cite{LiWang}.
