Synovial microenvironment (SME) plays a vital role in the formation of synovial pannus and the induction of cartilage destruction in arthritis. In this work, a concept of the photocatalytic regulation of SME is proposed for arthritis treatment, and monodispersive hydrogen-doped titanium dioxide nanorods with a rutile single-crystal structure are developed by a full-solution method to achieve near infrared-photocatalytic generation of hydrogen molecules and simultaneous depletion of overexpressed lactic acid (LA) for realizing SME regulation in a collagen-induced mouse model of rheumatoid arthritis. Mechanistically, locally generated hydrogen molecules scavenge overexpressed reactive oxygen species to mediate the anti-inflammatory polarization of macrophages, while the simultaneous photocatalytic depletion of overexpressed LA inhibits the inflammatory/invasive phenotypes of synoviocytes and macrophages and ameliorates the abnormal proliferation of synoviocytes, thereby remarkably preventing the synovial pannus formation and cartilage destruction. The proposed catalysis-mediated SME regulation strategy will open a window to realize facile and efficient arthritis treatment.