The collisional energy transfer reaction, O(D-1) + N-2 --> O(P-3) + N-2(v,J), has been studied by means of the ab initio MO and quasi-classical trajectory calculations. The ab initio MO calculations showed that the singlet surface [O(D-1)+N-2] is composed of the attractive potential curve where a strongly bound intermediate complex N2O is formed in the potential basin, whereas the triplet surface [O(P-3)+N-2] is composed of the repulsive shape. Both surfaces were crossed at region of around r(O-N) = 1.9 Angstrom and formed the seam of the conical intersection. By using the fitted ab initio PESs, three-dimensional surface-hopping trajectory calculations are performed. The calculated rotational and vibrational state distributions of the product N-2-(v,J) were composed of two components due to the contributions from both direct and complex channels. The branching ratio of direct channel to complex one increased linearly with collision energy. This is due to the fact that number of trajectories via complex channels is significantly diminished with collision energy because of less contribution from complex channels at higher collision energy. The mechanism of the energy transfer was discussed on the basis of the theoretical results.