The invention relates to a light intensity-adjustable energy-saving ultraviolet disinfection device. The device comprises an ultraviolet disinfection lamp; the ultraviolet disinfection lamp is a bismuth-indium-mercury alloy ultraviolet lamp; the device is provided with a dimming electronic ballast and a dimming module; and the dimming electronic ballast receives dimming signals sent by the dimmingmodule and adjusts the output light intensity of the ultraviolet disinfection lamp according to the dimming signals. The efficiency and power regulation performance of the ultraviolet disinfection device can be remarkably improved; the power of the ultraviolet disinfection device is regulated according to a water supply amount, so that energy consumption is reduced; the output linearity of the device is good; the stability of the function of a lamp tube is improved; the service life of the lamp tube is prolonged; and the efficient ultraviolet lamp and the dimming electronic ballast matched with the efficient ultraviolet lamp are adopted, so that the device has high efficiency.