BixOyBrz photocatalysts display great application potential in the field of organic pharmaceutical wastewater treatment, but the high recombination rate of photogenerated electron-hole pairs limits their application. In this work, Ti3C2 with excellent electron transfer performance was selected as a cocatalyst. Firstly, Ti3C2-Ru cocatalyst was prepared by taking full use of abundant surface Ti vacancy defects and high reduction ability of Ti3C2, then Bi4O5Br2/Ti3C2-Ru composite photocatalysts were prepared by realizing in-situ growth of Bi4O5Br2 on Ti3C2-Ru surface through the ionic bonding force between Ti3C2 surface functional groups and Bi3+. This special structure ensures the directional transfer of electrons from Bi4O5Br2 to Ti3C2 and then to the reaction active site of Ru, thereby the composite catalysts exhibit higher photogenerated carrier separation rate and lower interfacial charge transfer resistance, which effectively inhibit the recombination rate of photogenerated electron-hole pairs. The photocatalytic performance of composite photocatalysts were evaluated by the sulfamethoxazole (SMX) degradation efficiency. The results reveal that the Bi4O5Br2/Ti3C2-Ru composite photocatalysts exhibit excellent photocatalytic performance on SMX degradation. The optimum removal efficiency of SMX reaches 95.1% under 75 min visible-light irradiation, which increase 36.9 percentage points of pure Bi4O5Br2 and 25.3 percentage points of Bi4O5Br2/Ti3C2, respectively. Finally, the underlying photocatalytic mechanism was elucidated based on the radical scavenging experiments and catalyst band structure. This results will provide a novel design idea for the construction of photocatalyst with pharmaceutical wastewater treatment capability.