Magnetic properties of the quasi two-dimensional centered honeycomb antiferromagnet <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>GdInO</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math>

The crystal structure and magnetic property of the single crystalline hexagonal rare-earth indium oxides GdInO$_3$ have been studied by combing experiments model calculations. two inequivalent Gd$^{3+}$ ions form centered honeycomb lattice, which consists triangular sublattices. dc susceptibility specific heat measurements suggest antiferromagnetic phase transitions at $T_\textrm{N1}$ = 2.3 K $T_\textrm{N2}$ 1.02 K. An inflection point is observed in isothermal magnetization curve, implies an up-up-down with a 1/3 plateau. We also observe large entropy change originated from frustration GdInO$_3$. By considering classical spin Hamiltonian, we establish ground state diagram, suggests that has weak easy-axis anisotropy close to equilateral triangular-lattice system. theoretical ground-state diagram may be used as reference NMR, ESR, or $\mu$SR future.