Abstract: Activated carbon was prepared by phosphoric acid activation method with corn stalks as raw materials. The carbon quantum dots(CQDs) were prepared by hydrothermal synthesis with the activated carbon as the carbon source. The CQDs/TiO₂ composite photocatalyst was prepared by CQDs and TiO₂ composite. CQDs were characterized by FT-IR, XPS, TEM, XRD andRaman spectroscopy, confirming that CQDs mainly contained C and O elements, and they existed in a combination of C-C/C＝C, C-O and C＝O. CQDs were mainly nano spherical particles with an average particle size of 3.1 nm, which were composed of graphitized carbon core and functional groups. Moreover, the fluorescence performance of CQDs showed that the optimal excitation wavelength was 315 nm and the emission wavelength was 435 nm with blue fluorescence emission. The successful preparation of CQDs/TiO₂ photocatalyst was confirmed by TEM and XPS, and the composite of CQDs and TiO₂ was connected by Ti-O-C. Through the comparative analysis of catalytic degradation performance of CQDs/TiO₂ and TiO₂ under UV light (365 nm), xenon lamp simulated sunlight and outdoor sunlight, the results showed that the catalytic performance of CQDs/TiO₂ was lower than pure TiO₂ under UV light. The catalytic degradation performance of CQDs/TiO₂ under visible light(simulated sunlight and outdoor sunlight) was superior to pure TiO₂, and the highest degradation rate was 99.51% after outdoor sunlight irradiation for 105 min, basically degraded completely.