The magnetic interactions as well as the microscopic origins of the spin-Hamiltonian(SH) parameters including a, g, and Δg for 6S(3d5) state ion in cubic symmetry crystal field, taking into account the spin-spin (SS), the spin-other-orbit (SOO), the orbit-orbit (OO) magnetic interactions besides the well-known spin-orbit (SO) magnetic interaction, have been investigated using the complete diagonalization method (CDM). It is shown that the SH parameters arise from the five microscopic mechanisms of SO coupling, SS coupling, SOO coupling, OO coupling, and SO-SS-SOO-OO combined coupling. The relative importance of the contributions of the mechanisms to the SH parameters are investigated. It is shown that the SO coupling mechanism and the SO-SS-SOO-OO combined coupling mechanism are the most important of these coupling mechanisms. The contributions from SS coupling mechanism, SOO coupling mechanism, OO coupling mechanism to the SH parameter are quite small but their combined effects (SO-SS-SOO-OO combined coupling mechanism) is appreciable. The zero-field splitting (ZFS) arises from the net spin quartet states as well as the combined effects between the spin doublet states and the spin quartets states whereas the Zeeman g (or Δg)factor arises from the net spin quartet states. The contributions to the SH parameters from the net spin doublet states are zero. It is found that the relations: a>0，a(-|Dq|)a(|Dq|)，g(-Dq)=g(Dq)，a(-Dq,-ξd, B, C)=a(Dq,ξd, B, C) and Δg(-Dq, -ξd, B, C)=Δg(Dq, ξd, B, C) always hold for the selected crystal field area.Illustrative evaluations are performed for the four typical materials. Mn2+: KZnF3, Mn2+: RbCdF3, Mn2+: MgO and Mn2+: CaO. Good agreement between the theoretical values and the experimental results are obtained.