The microscopic origin of neutron spin resonance remains one of the major debates in iron-based superconductors. The spin resonance in iron pnictides is generally interpreted as a spin exciton arising from sign-reversed quasiparticle excitations between hole (at Г point) and electron (at X and Y points) Fermi surfaces. Our recent study on detwinned electron-doped NaFe0.985Co0.015As has revealed that he spin resonance in this system is dominated by the interband scattering with only dyz orbitals. Because of the differences between various iron-pnictide systems (such as structure and Fermi surfaces), the symmetry and orbital character of the spin resonance modes in other systems are still unclear and remain to be explored experimentally. Therefore, we propose to explore the orbital character of the spin resonance mode in electron-underdoped Ba(Fe1-xCox)2As2.