Abstract: Based on optical parameter data of different lake regions from 2001 to 2002 obtained in situ,the zonal distribution, the seasonal variation,the vertical distribution and the daily variation feature of beam attenuation coefficient are analyzed and the causes are explained.The attenuation coefficient,concentrations of chlorophyll-a(Chl-a) and total suspended matter (TSM) of Taihu Lake water and of some abroad lakes water are contrasted,which detailedly expounds the optical properties of Taihu Lake water body.The results show that the zone distribution of beam attenuation coefficient is estuary > Wuli Lake > Lake center,Lake center > Meiliang Lake,Meiliang Lake > Gonghu Lake,and Gonghu Lake > Easter Taihu Lake; the seasonal variations are different because the main affecting factors of beam attenuation coefficient at different zones are different; the beam attenuation coefficient at noon is bigger than that of morning and afternoon; there are two types of beam attenuation coefficient vertical distribution,one of which decreases step by step,the other decreases at first and varies little then; and the spectral properties of beam attenuation coefficient show that it is bigger at short wavelength than that of long wavelength and with a high value at 670nm.