  We report the $^{23}$Na and $^{75}$As NMR studies on NaFeAs single crystals.
The structure transition temperature $T_S$ (55 K) and the spin density wave
(SDW) transition temperature $T_{SDW}$ (40.5 K) are determined by the NMR line
splits. The spin-lattice relaxation rates indicate that the spin fluctuations
are strongly enhanced just below $T_S$ and drive a second order SDW transition.
A fluctuating feature of the SDW ordering is also seen below the $T_{SDW}$. We
further performed high-pressure NMR studies on NaFeAs, and found that the
$T_{SDW}$ increases by $\sim$7 K and the magnetic moment increases by 30% under
2.5 GPa pressure.
