The invention discloses a method for preparing a multiwall carbon nanotube-supported titanium dioxide catalyst, which belongs to the field of photochemical catalyst materials. The method comprises the following steps: adding multiwall carbon nanotubes and titanium sulfate into methanol respectively, and dispersing by ultrasonic waves and magnetic stirring; performing a solvothermal reaction, namely preparing a nano composite material by a solvothermal process to obtain the multiwall carbon nanotube-supported titanium dioxide catalyst; repeatedly washing the multiwall carbon nanotube-supportedtitanium dioxide catalyst, and drying under vacuum to obtain supported catalyst solid powder; dispersing the solid powder by ultrasonic waves and magnetic stirring, and preparing TiO2/MWCNT by a hydrothermal process; and repeatedly washing the obtained TiO2/MWCNT to obtain the multiwall carbon nanotube-supported titanium dioxide catalyst. In the TiO2/CNT prepared by the method, the TiO2 is selectively and uniformly loaded on the surface of CNT. The method combining the solvothermal and hydrothermal processes has the advantages of simplicity, high maneuverability and the like.