Deep eutectic solvents (DES) doping is an important method to realize the preparation and modification of PEDOT:PSS films in aqueous solution, but there is no systematic research focusing on its action mechanism in polymerization process. A series of in-situ characterizations were conducted to investigate the effect of DES doping on properties and structure. The UV–Vis spectra indicated the DES doping can strengthen the π−π* stacking interaction and conjugation stabilization of PEDOT:PSS, and then lead to stronger photovoltaic conversion ability. The in situ FTIR spectra revealed the hydrogen bonds were incorporated into the polymer chain during polymerization process. The CV and SEM analysis results suggested that DES doping delayed passivation nucleation stage of PEDOT:PSS film in the thickness direction and remained a stable polymerization rate. The XPS spectra of S 2p proved DES doping decrease the interaction between PEDOT and PSS. Comprehensive experiments demonstrate that the structure-induced effects of DES can trigger structural reorganization in line conformation of PEDOT:PSS/DESs. It is structure-induced effects of DES that delays passivation nucleation stage in polymerization and improves the optical absorption contrast, maximum current density and some other properties efficently.