  We study the canonical stability of a smooth projective 3-fold $V$ of general
type. We prove that
  (1) $|5K_V|$ gives a birational map onto its image provided the geometric
genus $p_g\geq 4$;
  (2) $|6K_V|$ gives a birational map provided $p_g=3$.
  Known examples show that both are optimal. This fact can be viewed as
parallel to surface case, though people know very little on 3-folds of general
type with $p_g\leq 1$.
