The variation features of phytoplankton pnmary production m spnng in Meiliang Bay of Lake Taihu is studied by means of dark and light bottle method (Winkler method).The aim is to study the daily change, vertical profile, region distribution d primary production, the relationship between chlorophyll-a and primary production, and the influence of incubation periods on photo-synthesis-irradiance curves.The results show that primary production of phytoplankton in Meiliang Bay presents a significant daily variation with a maximum during 10:00-14:00, accounting for 60% of daily primary production.The value of primary production during a 24h incubation period is largeiy lower than the sum of a 4h im ubation period.It is suitable to calculation the daily total primary production using the value during !0:00-14:00.Pnmary production decreases from inner Meiliang Bay to outer Meiliang Bay due to the difference of chlorophyll-a and concentration of nutrients.Primary production basically decreases with the increase of water depth with an exception at surface layer water due to photoinhibition.A significant positive linear relationship is found between primary production and concentration of chlorophyll-a of surface layer water, concentration of chlorophyll-a in a water column.It is obvious that primary production can be precisely estimated with concentration of chlorophyll-a in a water column.Shorter light incubation time always causes high primary production and assimilation number.