The invention discloses a method for treating sewage by using a titanium dioxide glass fiber mesh-electrospun composite nanofiber membrane. The method comprises the following steps: fully infiltratinga pretreated glass fiber mesh in a titanium dioxide colloid, vertically and uniformly pulling out the glass fiber mesh to completely leave the colloid, naturally drying the infiltrated glass fiber mesh at room temperature in a ventilated environment, carrying out high-temperature sintering treatment in a box-type resistance furnace, naturally cooling the sintered glass fiber mesh to room temperature, continuously performing coating and sintering, and repeating above operations to obtain a silica glass fiber mesh; performing electrospinning by adopting a horizontal electrospinning device, extracting a polymer spinning solution by a syringe, connecting the needle of the syringe with the positive electrode of a high-voltage generator, applying a voltage, and grounding a receiving device; andvertically immersing immersion ultraviolet lamps in a liquid storage tank filled with a sewage solution, and vertically mixing the obtained titanium dioxide glass fiber mesh and the obtained electrospun composite nanofiber membrane between the ultraviolet lamps to treat the sewage.