In the past 20 years, the decrease in stratospheric ozone concentrations has provoked an increase of UV-B radiation in the wavelength range from 280 to 320nm. The ecological effects of increased UV-B on global environment attract more and more scientific studies. This paper demonstrates the advances of effects of UV-B radiation on aquatic organisms and aquatic ecosystems in lakes. The penetration of UV-B radiation into lakes is highly dependent on the concentration of dissolved organic carbon (DOC) and chromophoric dissolved organic matter(CDOM) in the water body. Many empirical regression relationships between the concentration of DOC and the diffuse attenuation coefficient, the euphotic depth (1% of surface irradiance) were found in many studies. Many studies demonstrate a variety of aquatic organism ranging from bacterioplankton and phytoplankton to zooplankton, and even aquatic vertebrates such as fish are vulnerable to damage from increased UV-B radiation. In general, aquatic organisms have three levels responses to minimize the exposure to UV-B: (1) behavioral avoidance, (2) manufacture or sequester UV-B absorbing compounds, (3) DNA repair mechanisms. Some assumptions about the effects of UV-B radiation on Lake Taihu ecosystem are presented. 