The authors study on condition and mechanism of eutrophication in Three Gorges Reservoir Area(TGRA) in Chongqing,aiming at the importance and complexity of nutrition restrictive factor and eutrophication.By AGP experiment,the nutrition restrictive factors of the Changjiang and Jialing Rivers interjunction is confirmed is confirmed.The experimental results show that: Single nitrogen is not an obvious stimulus to growth of algae,while phosphorus acts as the limiting factor of that;When TN/TP is high,the standing crop of algae is small;when TN/TP is low,the standing crop of algae is large;The concentrate of phosphorus in the water is higher,the effect accelerating algae and increaseing through adding phosphorus is more strong.The experimental results provide us with important parameters to understand the conditions of eutrophication and analyse its mechanism.