Quantum spin state transitions in the spin-1 equilateral triangular lattice antiferromagnet <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Na</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mi>BaNi</mml:mi><mml:msub><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mi>PO</mml:mi><mml:mn>4</mml:mn></mml:msub><mml:mo>)</mml:mo></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>

We have grown single crystals of ${\mathrm{Na}}_{2}\mathrm{BaNi}{({\mathrm{PO}}_{4})}_{2}$, a spin-1 equilateral triangular lattice antiferromagnet (ETLAF), and performed magnetic susceptibility, specific heat, thermal conductivity measurements at ultralow temperatures. The main results are as follows: (i) At zero field, ${\mathrm{Na}}_{2}\mathrm{BaNi}{({\mathrm{PO}}_{4})}_{2}$ exhibits ordering 430 mK with weak ferromagnetic moment along the $c$ axis. This suggests canted ${120}^{\ensuremath{\circ}}$ spin structure, which is in plane including crystallographic axis due to existence an easy-axis anisotropy ferromagnetically stacked (ii) With increasing field axis, 1/3 magnetization plateau observed, means that structure transformed into up-up-down (UUD) structure. even higher fields, UUD phase further evolves possible V ${\mathrm{V}}^{\ensuremath{'}}$ phases. (iii) $a$ possibly umbrella phase. Therefore rare example ETLAF single-crystalline form series quantum state transitions.