  Topological nodal-line semimetals with exotic quantum properties are
characterized by symmetry-protected line-contact bulk band crossings in the
momentum space. However, in most of identified topological nodal-line
compounds, these topological non-trivial nodal lines are enclosed by
complicated topological trivial states at the Fermi energy ($E_F$), which would
perplex their identification and hinder further applications. Utilizing
angle-resolved photoemission spectroscopy and first-principles calculations, we
provide compelling evidence for the existence of Dirac nodal-line fermions in
the monoclinic semimetal SrAs$_3$, which are close to $E_F$ and away from
distraction of complex trivial Fermi surfaces or surface states. Our
calculation indicates that two bands with opposite parity are inverted around
\emph{Y} near $E_F$, which results in the single nodal loop at the
$\Gamma$-\emph{Y}-\emph{S} plane with a negligible spin-orbit coupling effect.
We track these band crossings and then unambiguously identify the complete
nodal loop quantitatively, which provides a critical experimental support to
the prediction of nodal-line fermions in the CaP$_3$ family of materials.
Hosting simple topological non-trivial bulk electronic states around $E_F$ and
no interfering with surface states on the natural cleavage plane, SrAs$_3$ is
expected to be a potential platform for topological quantum state investigation
and applications.
