Phyllodiaptomus tunguidus, a large calanoids, is Chinese endemic species, and mainly distribute in South China. To understand its population distribution in a large scale, the species was sampled twice in 19 middle and large reservoirs of Guang-dong Province in 2000 and five times in two large and oligotrophic waterbodies; Liuxihe Reservoir and Xinfengjiang Reservoir in 2002. Body size and other morphological parameters of P. tunguidus were measured in the Liuxihe Reservoir, Xinfengjiang Reser-voir and Hedi Reservoir(large and mesotrophic).Adult P. tunguidus was found in 11 reservoirs, but only occurred in 6 reservoirs in both flood and dry seasons. P. tnngnidus had an average abundance of 0. 465 ind. /L and 0. 996ind. /L in the flood and dry sea-sons, respectively. In 2002, the average abundance was 1. 308ind. /L and 0. 294ind. /L in Liuxihe Reservoir and Xinfengfang Reservoir, respectively. The abundance in the flood season was much higher than that in the dry season. P. tunguidus mainly dis-tributed in larger reservoirs, dominated in large, oligotrophic reservoirs, and its abundance was mainly determined by focal concen-tration, food quality and predation pressure. The first antennule length and body size of the individual adults were longer in oligo-trophic waterbodies than that in the mesotrophic waterbody. Predation by filter and planktivory fishes may be the main selection force.