Herein, the design and synthesis of a multifunctional (Fe3O4-NaYF4:Yb,Tm)@TiO2 photocatalyst through a facile sol-gel process combined with electrostatic self-assembly has been reported. Particularly, as an upconversion sensor, NaYF4:Yb,Tm nanoparticles have the ability to convert near-infrared (NIR) light into ultraviolet (UV) emissions, so that the catalytic body TiO2 can indirectly utilize the NIR part of sunlight but not UV light. The excellent photocatalytic activity of the hybrid samples is evaluated using a model of the degradation of methylene blue (MB). Most importantly, the obtained materials exhibit remarkable magnetic properties because of the addition of a magnetic component (Fe3O4), therefore, the photocatalysts possess desired recyclability and reusability, which is significant for actual applications. Finally, the possible photocatalysis mechanism of the nanohybrids is discussed and hydroxyl radicals (OH˙) are confirmed as the main reactive species.