The invention discloses an online detection apparatus for detecting water quality of river water. The online detection apparatus comprises a shell, wherein the shell is a cylindrical fusiform structure, one side of the shell is provided with a first water flow generator, the other side of the shell is provided with a second water flow generator, and the first water flow generator and the second water flow generator are symmetric about an axis of the shell; and the bottom of the shell is provided with a water quality detection sensor. By adopting the online detection apparatus, the water quality state of the river water can be regularly detected at a fixed point; by arranging a fixed apparatus and a noose, the depth regulation of the device can be realized, the river water at different depths can be detected, and rapidness in detection and convenience and usability can be realized; and by adopting a solar panel and the water flow generators, the complementary utilization of optical energy and water energy is realized, the downtime of the detection apparatus caused by the shortage of sunlight or slowing of the water flow can be reduced, and the stability and working efficiency of the device can be improved.