On January and July of 2003, vertical distribution pattern of zooplankton in Baushan Reservoir was observed. Sampling was carried out last for 24-48 hours in 5 layers (0-1m, 1-2m, 2-5m, 5-9m and 9-14m) during each 2 hours period. The zooplankton was dived into 8 groups (Rotifer, copepod nauplius, copepodite stages of copepod, Bosmina longirostris, Diaphanosoma dubium, Neodiaptomus schmackeri, hermocyclops taihokuensis, Tropocyclops prasinus berviroamus), vertical distribution of them during day and night were compared to understand their diel vertical migration patterns.According to the WMD (Weighted Mean Depth) value, only Diaphanosoma dubium had significant diurnal vertical migration in both seasons and Tropocyclops prasinus berviroamus with significant diurnal vertical migration in winter. The other groups of zooplankton were without such pattern in significance. The principle component analysis was employed to abstract the information of environmental factors for each sampling point. Two factors were abstracted with 96% of variances, the first was physical factor with higher loading of temperature, and the second was food factor with higher loading of chlorophyll a.
