  Let $X$ be a minimal projective 3-fold of general type. The pluricanonical
section index $\delta(X)$ is defined to be the minimal integer $m$ so that
$P_{m}(X)\geq 2$. According to Chen-Chen, one has either $1\leq \delta(X)\leq
15$ or $\delta(X)=18$. This note aims to intensively study those with maximal
such index. A direct corollary is that the $57$th canonical map of every
minimal 3-fold of general type is stably birational.
