  We investigate a text-book mixed-anion compound SrVO$_2$H using
first-principles calculation, to theoretically pin down the factors that
stabilize its anion ordering. We find that the $trans$ preference by the
characteristic crystal field in the VO$_4$H$_2$ octahedron in addition to a
coherent shrinkage along the V-H-V direction, taking place when such direction
is consistent among neighboring hydrogens, stabilize the anion ordering
observed in experiment. Our study gives an important clue for controlling the
anion ordering in transition metal oxyhydrides.
