Abstract：Efficient reverse intersystem crossing (RISC) is one of the most effective ways to achieve high exciton utilization of pure organic electroluminescent materials. There are two factors affecting the RISC rate (kRISC): the energy difference between the singlet and triplrt excited states (ΔES-T) and the spin-orbit coupling (SOC) between the excited states. In this article, based on the theoretical calculation method which can accurately and quantitatively describe the excited state of the molecule, the typical D-A molecule TPA-NZP is used as a template to study the change of the ΔES-T and the SOC by adjusting the twisting angle of the donor and acceptor in the molecule. By studying the relationship between the excited state transition properties and the SOC, we find that different transition states have a great influence on the coupling. The two excited states are both LE states, but if the phase of the electron cloud are different, which will cause the SOC between them increased greatly; when the transition is the CT state, the SOC matrix elements between the LE state and the CT state both very small; when the singlet and triplet transitions occur in the same part, but the direction of the transition is changed may lead to a huge increase in the SOC.