In unconventional superconductors, the major challenge on the mechanism research is to reveal how the electrons form to Cooper pairs and collectively condense to a superconducting state under both interactions from charge and spin. The iron-based superconductors are similar to those copper oxide and heavy fermion superconductors, and they also exhibit strong spin fluctuations, which likely promote the superconducting pairing by acting as the bosonic "pairing glue." Such argument is supported by a spin resonance mode with a peak energy universally linear scaling with Tc. However, it is still unknow whether in such multi-orbital systems the spin system may have some preferred fluctuating directions that is coupled to the orbital degree of freedom.