The debate whether interband or intraband scattering is crucial for Fe-based superconductors is not settled down yet. Investigation a system with completely missing electron pockets or hole pockets will be important to clarify this controversy. KFe2As2 is such kind of idea system in which electron pocket at M point is completely replaced by hole pockets. We plan to map out the incommensurate magnetic excitations first and study the temperature dependence of the spin excitations at low energy range.