  Topological nodal line semimetals, hosting one-dimensional Fermi lines with
symmetry protection, has become a hot topic in topological quantum matter. Due
to the breaking of time reversal symmetry in magnetic system, nodal lines
require protection by additional symmetries. Here, we report the discovery of
antiferromagnetic type-I and type-II nodal lines coexist in the monolayer
CrAs$_{2}$ based on a systematic first-principles calculation. Remarkably, the
type-I nodal line in CrAs$_{2}$ form a concentric loop centered around the
$\Gamma$ point is filling-enforced by nonsymmorphic analogue symmetry and
robust against spin-orbital coupling. The type-II nodal lines, a kind of open
nodal lines appear around the Fermi level, are protected by the mirror symmetry
in the absence of spin-orbital coupling. The antiferromagnetic monolayer
CrAs$_{2}$ proposed here may provide a platform for the correlation between
magnetism and exotic topological phases.
