In this study, Nb2O5 nanorods/graphene composites (NbO NRs/GR) are prepared by one-pot alkaline hydrothermal process, utilizing the new roles of graphene oxide (GO) as the structure-directing and morphology-controlling agent for the growth of NbO NRs. Compared to blank NbO, NbO/GR composites exhibit significantly improved photocatalytic activity for 4-CP degradation under visible-light irradiation, although 4-CP and NbO do not absorb visible light themselves. The in-situ formation of surface complexes between 4-CP and NbO and the subsequent charge transfer based on LMCT mechanism can be responsible for the visible photocatalytic activity. And meanwhile, the photoelectrons transferred to GR surface from in-situ formed complex (NbO/4-CP) via NbO NRs can initiate the synergistic Cr(VI) reduction. The GR contents and NbO crystalline phase have great effects on the photocatalytic activity of NbO/GR composites toward simultaneous 4-CP degradation and Cr(VI) reduction. The amorphous NbO/GR composite with 4.0 wt% GR (NbO-400/GR-4.0%) shows the highest photocatalytic activity. The influences of various experimental conditions (including the surface fluorination of NbO/GR, the initial concentrations of 4-CP and Cr(VI), pH, reaction atmosphere, and adding radical scavengers) on the visible photocatalytic activities are investigated in detail. According to the catalytic activity, UV-vis DRS and FT-IR spectra of NbO/4-CP or NbO/GR/4-CP, and photocurrent response in aqueous 4-CP solution, the formation of the surface complex is evidenced and the visible-light catalytic mechanism based on LMCT process is proposed.