  Nuclear spin polarization plays a crucial role in quantum information
processing and quantum sensing. In this work, we demonstrate a robust and
efficient method for nuclear spin polarization with boron vacancy
($\mathrm{V_B^-}$) defects in hexagonal boron nitride (h-BN) using ground-state
level anti-crossing (GSLAC). We show that GSLAC-assisted nuclear polarization
can be achieved with significantly lower laser power than excited-state level
anti-crossing, making the process experimentally more viable. Furthermore, we
have demonstrated direct optical readout of nuclear spins for $\mathrm{V_B^-}$
in h-BN. Our findings suggest that GSLAC is a promising technique for the
precise control and manipulation of nuclear spins in $\mathrm{V_B^-}$ defects
in h-BN.
