Abstract: The ultraviolet distribution in the waters of Meiliang Bay and MAAs concentration in algae was studied,and the results showed that the ratio of ultraviolet to PAR was relatively low in Jan.-Mar.,and relatively high in July,maintained at certain level in other months of the year;DOC concentration changed greatly in different season;CDOC has significant effects on the attenuation of UV;there was great amount of MAAs in algae and has been identified as shinorine and porphyra-334 by using UV scan and HPLC.