Environmental pollution, particularly water contamination, is regarded as one of the most crucial global problems, where a semiconductor photocatalyst towards organic pollutant degradation driven by photocatalysis is a promising technique. Herein, novel Eu-TiO2-GO composites with excellent photocatalytic performance were fabricated via simple and green sol-gel technique. In addition, density functional theory (DFT) method was employed to investigate the electronic structure, stability and charge transfer of the composites. The experimental study revealed that the optimal performance was obtained with the Eu-TiO2-GO (0.6% Eu) composite, of which the apparent rate constant was about 19-folds higher than that of bulk TiO(2)because of the combined effects of better visible light absorbance and efficient separation of charge carriers. The efficiency of Eu-TiO2-GO (0.6% Eu) in the degradation of indigo carmine (IC) dye reached 96.78% in 60 min under light irradiation. Based on the DFT method, we observe an efficient electron-hole pair separation, a potential drop and an in-built polarised electric field at the interface of Eu-TiO2-GO composite. Remarkably, Eu-TiO2-GO composite was found to exhibit a stronger interfacial interaction, smaller interlayer distance and a larger redistribution of charge than TiO2-GO composite. The stability and reusability of Eu-TiO2-GO (0.6% Eu) composite as an effective solar photocatalyst was confirmed by five cycling tests of wastewater treatment. From radical quenching experiments, hydroxyl and superoxide radicals were the dominant active species for the photodegradation reaction of IC dye. All these findings may shed light on the intrinsic reasons for the improved degradation of pollutants.