It is highly desired to improve the photocatalytic activities of In2O3 for degrading pollutants by increasing reactant adsorption, enhancing the charge separation and promoting oxygen activation. Herein, porous In2O3 with high photocatalytic activity for degrading pollutants has successfully been synthesized by an In(OH)(3) precursor route with citric acid as the modifier, and its photoactivities could be further improved by coupling with CuO through a simple impregnation process, especially with the K-modified one. The amount-optimized K-modified CuO/In2O3 nanocomposite exhibits a rather high photocatalytic activity for degrading 2,4-di-chlorophenol (2,4-DCP), with similar to 3-time enhancement than the bare In2O3. It is attributed to the effective charge separation and the promoted O-2 activation by coupled K-modified CuO mainly based on the surface photovoltage spectroscopy, transient state surface photovoltage, O-2 temperature-programmed desorption and electrochemistry results. In addition, radical-trapping experiments show that the produced center dot O-2(-) is dominant to induce the photocatalytic degradation of 2,4-DCP, implying that the developed modulation strategy to photo-generated electrons is much feasible compared to holes. This work offers an effective strategy to design and synthesize high-activity In2O3-based nanophotocatalysts for degrading pollutants.