Liuxihe Reservoir, located at the tropic of Cancer, is a large valley-type reservoir. In order to understand its limonological features, main limnological variables including hydrological and environmental factors were observed monthly in 2006. Surface water temperature ranged from 14.9 to 31.6 . The thermal stratification ℃ ℃ was monomictic, initiating in the early March when the water temperature reached 20 , and lasting until December. The total precipitation in 2006 was 2960mm, but mainly distributed in ℃ wet season (from April to September). The mean water residence time was about 170 days, being more short in the flooding season (65 days). The mean concentrations of TN, TP, chlorophyll-a and SD were 0.66mg/L, 0.016mg/L, 2.2mg/m³ and 3.1m, respectively, indicating that the reservoir was oligo-mesotrophic. Mass ratio of TN/TP is around 41, 78 for DIN/DIP. Both ratios were much higher than the Redfield ratio, and mean that growth of phytoplankton was strongly limited by phosphorus. The high N/P ratio was attributed to the tropical red soil containing rich iron. A distinct longitudinal pattern and seasonal variability in limnological variables were observed in this reservoir. At the beginning of wet season (April and May), all nutrient concentrations were significantly higher than other period. It confirmed that surface runoff was the main path for nutrient loading into the reservoir. The longitudinal pattern of nutrient and chlorophyll-a concentrations was typical as follows as riverine zone>transition zone>lacustrine zone, and the water transparency correspondingly showed an opposite one. High inflow with monsoon was the main driving force in seasonality oflimnological variables, and resulted finally in a significantly longitudinal gradient of these variables by interacting with the reservoir own morphology.