Abstract: Based on the investigations on primary productivity and related factors at one fixed stations in Guanzhuangping Bay ofXiangxi River from February to April 2005,this paper studied the temporal and spatial distribution of chlorophyll a,primary productivity,and their relationships with change of ray radiation intensity in water.Although the results showed that there were obvious same periodic change appeared 5 peak value and were 7-10 days interval averagely,not synchronization in chlorophyll a andprimary productivity in the each layer of water. The true light layer depth that was lied intervenient the lake and ocean,was as10m water depth or so at Guanzhuangping Bay,the light compensates to order for the 4-5mwater depth. The high values of primary productivity were confirmed in 015 underwater,and one of chlorophyll a content was 2mwater depth. The vertical change ofwater temperature showed that the obvious difference was recorded at latter days. There were significant positive correlation between increment daily average temperature (ΔT·d-1) and average gross primary productivity,net primary productivity in every water layer.The investigation also made us know more about the unique characteristics of the river ecosystem’s primary productivity,differ from other types water body in Guanzhuangping Bay of Xiangxi River in Sanxia reservoir. With the strengthen of the stronglight,the primary productivity of the initial stage (bottomfloor) increases with small extent ;when the light strengthen rises to over50 (μmol/m2·s),the increasing extent of the primary productivity was enlarged. This changing trend was different from that oflakes. The result of 17 group data measured before April 10 showed that the temperature in different water layer does not have significant difference. So,in the lowwater temperature season,the perpendicularity of the temperature has minor influence on the primary productivity.Because of“enwraping effect”of the existing chlorophyll,there is no significant relationship between the perpendicularity of chlorophyll and the primary productivity. The chlorophyll density has the same periodic as the variety of eachlayer of water,both including 5 peak value. The each average period was about 7-10 d ;The entrylevel produces also have theperiodic changes,with the times of existing crests same as that of chlorophyll,yet did not exit at the same time. However,based onthe acquired data,we can’t clearly analy