The local structure distortion, the spin Hamiltonian (SH) parameters, and the electric fine structure of the ground state for Mn2+(3d5) ion in ZnO crystals are systematically investigated, where spin-spin (SS), spin-other-orbit (SOO) and orbit-orbit (OO) magnetic interactions, besides the well-known spin-orbit (SO) coupling, are taken into account for the first time, by using the complete diagonalization method. The theoretical results of the second-order zero-field splitting (ZFS) parameter D, the fourth-order ZFS parameter (a-F), the Zeeman p-factors: g// and g⊥ and the energy differences of the ground state: δ1 and δ2 for Mn2+ in Mn2+: ZnO are in good agreement with experimental measurements when the three O2- ions below the Mn2+ ion rotate by 1.085° away from the [111]-axis. Hence, the local structure distortion effect plays an important role in explaining the spectroscopic properties of Mn2+ ions in Mn2+: ZnO crystals. It is found for Mn2+ ions in Mn2+: ZnO crystals that although the SO mechanism is the most important one, the contributions to the SH parameters, made by other four mechanisms, i.e. SS, SOO, OO, and SO～SS～SOO～OO mechanisms, are significant and should not be omitted, especially for calculating ZFS parameter D.