This paper based on the conventional monitoring data from in 2005–2007, and studied the distributing of chlorophyll-a with temporal and spatial distribution, and the relationship between the chlorophyll-a and TN, TP concentrations. The results showed that chlorophyll-a concentration appeared obvious temporal and spatial changes, and the values were arranged according to May>July, August>October>September>June. Chlorophyll-a concentration of May and October higher than others. The supply water of Lake Ulansuhai occurred form drainage of Hetao in May and October, and there is a lot of nutrition was bring into Lake Ulansuhai, which induced growth of algae. By analyzing, the relationships between chlorophyll-a concentration and TN and TP concentration appeared evidently in May and October of 2006, and the relationships in August were not remarkable, and no relationship in other months