  Ultraflat bands have already been detected in twisted bilayer graphene and
twisted bilayer transition-metal dichalcogenides, which provide a platform to
investigate strong correlations. In this paper, the electronic properties of
twisted trilayer molybdenum disulfide (TTM) are investigated via an accurate
tight-binding Hamiltonian. We find that the highest valence bands are derived
from the $\Gamma$-point of the constituent monolayer, and they exhibit a
graphenelike dispersion or become isolated flat bands that are dependent on the
starting stacking arrangements. The lattice relaxation, local deformation, and
external fields can significantly tune the electronic structures of TTM. After
introducing the spin-orbital coupling effect, we find a spin-valley-layer
locking effect at the minimum of the conduction band at the $K$- and
$K^\prime$-point of the Brillouin zone, which may provide a platform to study
optical properties and magnetoelectric effects.
