Exploring the macroscopic quantum effect of a frustrated quantum magnet has been one of the main subjects of condensed matter physics. Ba3CoSb2O9 approximates the two-dimensional S=1/2 triangular-lattice Heisenberg antiferromagnet, which is a paradigmatic example of the rustrated quantum magnet. T Ba3CoSb2O9 exhibits magnetic-field-induced quantum phase transitions including 1/3-magnetization plateau state, which arise from the synergy between spin frustration, quantum fluctuation and weak interlayer exchange interaction. Although all the spin structures in the field-induced quantum phases were theoretically predicted, the experimental verification has not been completed. We propose single crystal neutron diffraction measurement on Ba3CoSb2O9, using HFM/EXED. One of the transitions occurs at 22.5 T, which can be accessed by only HFM/EXED.