Carbon nanodots(CDs) with visible absorption band and TiO_2 are integrated to enhance the photosensitivity of TiO_2.The CD/TiO_2 nanocomposites show obvious CD-coverage-dependent photocatalytic performance. The CD/TiO_2 nanocomposites with moderate CD coverge exhibit the highest photocatalytic activity after being irradiated with visible light, which is more excellent than that of TiO_2. Too little CD coverage could result in poor visible light absorption, which limits the photocatalytic performance of CD/TiO_2 nanocomposites. While, too much CD coverage weakens the photocatalytic activity of CD/TiO_2 nanocomposites by restraining the extraction of conduction band electrons within TiO_2 to generate active oxygen radicals and the electron transfer(ET) process from CDs to TiO_2. These results indicate that rational regulation of CD coverage and the realization of efficient ET process are important means to optimize the photocatalytic performance of CD/TiO_2 nanocomposites. Carbon nanodots (CDs) with integrated absorption band and TiO 2 are integrated to enhance the photosensitivity of TiO 2. The CD / TiO 2 nanocomposites show obvious CD-coverage-dependent photocatalytic performance. The CD / TiO 2 nanocomposites with moderate CD coverge exhibit the highest photocatalytic activity after being irradiated with visible light, which is more excellent than that of TiO 2. Too little CD coverage could result in poor visible light absorption, which limits the photocatalytic performance of CD / TiO 2 nanocomposites. While, too much CD coverage weakens the photocatalytic activity of CD / TiO_2 nanocomposites by restraining the extraction of conduction band electrons within TiO_2 to generate active oxygen radicals and the electron transfer (ET) process from CDs to TiO_2. These results indicate that rational regulation of CD coverage and the realization of efficient ET process are important means to optimize the photocatalytic performance of CD / TiO 2 nanocomposites.