Organic synthesis methods initiated by visible light have received increasing attention from synthetic chemists. Reactions initiated by EDA complexes do not require the use of toxic or expensive photoredox catalysts compared to traditional photoreaction processes. However, this kind of reaction requires the structure of the substrate, so it is important to study the detailed and systematic reaction mechanism for its design. The EDA complexes of substituted 1 H-indole and substituted benzyl bromide derivatives were studied by density functional theory (DFT). The difference between EDA complexes with substituents of different kinds and locations were compared by theoretical study and new EDA complex was predicted.