Ba3CoSb2O9 approximates the two-dimensional S=1/2 triangular-lattice Heisenberg antiferromagnet, which exhibits aboundant macroscopic quantum effect. it experiences fascinating magnetic-field-induced quantum phase transitions including 1/3-magnetization plateau, distorted and staggered coplanar phase, which are resulted from spin frustration, quantum fluctuation and weak interlayer exchange interaction. Although all the spin structures in the field-induced quantum phases were theoretically predicted and experimentally verified by various means, it still remain some unsolved debates, especially along the c axis, which is to some extent overlooked. Recently we have convincingly verified the spin structure using neutron diffraction in high field in ab-plane. Based on our oreviuous experiments, We propose a single crystal neutron diffraction measurement with field along c axis, using HFM/EXED. All expected phases upon field can be reached and invesitgated before saturation on EXED.