The crystal structure and magnetic property of the single crystalline hexagonal rare-earth indium oxides GdInO3 have been studied by combing experiments and model calculations. The two inequivalent Gd3+ ions form the centered honeycomb lattice, which consists of honeycomb and triangular sublattices. The dc magnetic susceptibility and specific heat measurements suggest two antiferromagnetic phase transitions at TN1=2.3K and TN2=1.02K. An inflection point is observed in the isothermal magnetization curve, which can be an indication of an up-up-down phase with a 1/3 magnetization plateau, further supported by our theoretical calculation. We also observe a large magnetic entropy change originated from the magnetic frustration in GdInO3. By considering a classical spin Hamiltonian, we establish the ground state phase diagram, which suggests that GdInO3 has a weak easy-axis anisotropy and is close to the equilateral triangular-lattice system. The theoretical ground-state phase diagram may be used as a reference in NMR, ESR, or μSR experiments in future.