  The antiferromagnetic (AFM) valleytronics can be intrinsically more
energy-saving and fast-operating in device applications. In general, the
lacking spontaneous spin-splitting hinders the implementation and detection of
anomalous valley Hall effect (AVHE). Here, we propose to implement AVHE in
electric-potential-difference antiferromagnetic $\mathrm{Cr_2CHCl}$ monolayer
with excellent stability, where the spontaneous spin-splitting can be induced
due to layer-dependent electrostatic potential caused by out-of-plane built-in
electric field. From a symmetry perspective, the introduction of Janus
structure breaks the combined symmetry ($PT$ symmetry) of spatial inversion
($P$) and time reversal ($T$), which gives rise to spin-splitting. Both
unstarined and strained monolayer $\mathrm{Cr_2CHCl}$ possess valley splitting
of larger than 51 meV, which is higher than the thermal energy of room
temperature (25 meV). The layer-locked Berry curvature gives rise to
layer-locked AVHE. Our work reveals a route to achieve AVHE in AFM monolayer
with spontaneous spin-splitting.
