The fluorescent spectrum and the excitation spectrum were used to present the cluster molecular structure feature in ethanol-water solutions. Through analyzing the fluorescent characteristics of an excimer, it is proposed that the excimers are formed between the ethanol-water cluster molecules in the excited state and in the ground state. The fluorescent lifetime and the fluorescent intensity decay process give information about the photo-physical and photo-chemical processes of the formation and the dissociation of an excimer. The theoretical calculation and physical analysis coincide with the experimental results. The preliminary conclusion about the structure feature of ethanol-water cluster molecule is that it has a planar one like a sandwich.