  An ideal 1H phase monolayer MoS$_2$ has the mirror reflection symmetry but
this symmetry is broken in common experimental situations, where the monolayer
is placed on a substrate. By using the k$\cdot$p perturbation theory, we
investigate the effect of the mirror symmetry breaking on the Berry curvature
of the material. We find that the symmetry breaking may modify the Berry
curvature considerably and the spin/valley Hall effect due to the modified
Berry curvature is in qualitative agreement with a recent experimental result
[Science $\bf 344$, 1489 (2014)], which cannot be explained by previous
theories that ignore the mirror symmetry breaking.
