The photocatalytic reduction experiments of Cr(VI) over the sulfate-modified titanium-bearing blast furnace slag photocatalyst under UV-vis light irradiation in the absence/presence of citric acid (0≤[citric acid]≤4 mM) were performed at different pH and different initial concentration. In the presence of citric acid, the photocatalytic reduction efficiency of Cr(VI) was significantly enhanced and kinetic constants of the compound system (in the presence of photaocatalyst, citric acid and Cr(VI))was nearly 9.2 times than that in the absence of citric acid. This enhanced efficiency may be attributed to the effective separation of electron-hole in the presence of citric acid. The maximum rate of Cr(VI) reduction was obtained for an initial citric acid/Cr(VI) molar ratio, R=3.75, a further increment in R being disadvantageous; however, the photocatalytic reduction efficiency of Cr(VI) in the presence of citric acid was always faster than in its absence. The synergistic effect factor is always greater than 6 in the compound system, indicating that a marked synergistic effect between the photocatalytic reduction of Cr(VI) and citric acid.