Ultra-low dielectric constant of nanoconfined water between two flat slabs is a subject of recent experimental and theoretical research. The impact of dissolution of sodium chloride (NaCl) with various concentrations on the dielectric properties of nanoconfined water between graphene layers are investigated using molecular dynamics simulations. We found that, with increasing salt concentration, (i) the out-of-plane dielectric constant increases and (ii) the in-plane dielectric constant decreases non-linearly. Surprisingly, for channels with heights 6.8 angstrom < h < 8 angstrom, we found an abnormal increase in the in-plane dielectric constant versus salt concentration, which can be linked to the formation of 2D-ice-like structure. This study sheds light on the variation of dielectric properties of nanoconfined water between graphene layers in the presence of salt, which is of importance in ion transport and electrochemical energy storage.