TiO2 doped with C was obtained by way of immersion and calcinations method by using citric acid (CA) as dopant material.，and characterized by using XPS、XRD, UV-Vis, FT-IR and SPS. The results of analysis and characterization showed that C substituted partial Ti atoms in the lattice of TiO2 and formed Ti-O-C structure. The photocatalytic properties of C-TiO2 photocatalysts had been evidently improved as a result of a noticeable shift to visible region and the enhancement of the charge separation efficiency. The doped carbon lowers the band gap and expends the absorption of visible light region. CO2 was photocatalytically reduced to form HCOOH by the best C-TiO2-3/1-600 nanoparticles under the irradiation of the simulated daylight lamp. Methanoic acid yield may achieve 2633.98μmol/g-Cat when irradiation time is six hours.