  The properties of the asymptotic $AdS_3$ space-times representing flat domain
walls (DW's) solutions of the New Massive 3D Gravity with scalar matter are
studied. Our analysis is based on $I^{st}$ order BPS-like equations involving
an appropriate superpotential. The Brown-York boundary stress-tensor is used
for the calculation of DW's tensions as well as of the $CFT_2$'s central
charges. The holographic renormalization group flows and the phase transitions
in specific deformed $CFT_2$ dual to 3D massive gravity model with quadratic
superpotential are discussed.
