A direct correlation between spin excitations and superconductivity in iron-based superconductors is the evolution of low energy spin excitations in the over-doped region.In BaFe2-xNixAs2 system, the low energy spin excitations decreased significantly upon Ni doping, and finally form a large spin gap up to 50 meV in the heavily over-doped non-superconducting BaFe1.7Ni0.3As2. While neutron scattering on the overdoped BaFe1.82Ni0.18As2 with Tc=8 K suggests that the low energy spin excitations persist to 5 meV at least. But it is still not clear for the formation of large spin gap in overdoped samples and whether it is related to the disappearance of superconductivity in overdoped regime. Therefore, we propose to do inelastic neutron scattering measurements on the heavily overdoped BaFe2-xNixAs2 around the superconducting zone boundary, mainly focusing on the low energy spin gaps. A comprehensive determination of spin gaps through the whole phase diagram will give us important information concerning the relationship between low energy spin excitations and superconductivity.