Abstract: Tonle Sap Lake is the largest and most influential freshwater lake in Southeast Asia. Based on Tonle Sap lake terrain data from multiple sources, the area and volume of Tonle Sap Lake under different water levels with 0.1m gradient are measured by the established irregular triangulation. Through comparative analysis and review by hydrological method, the results show that the built water level - area (volume) correlation is reasonable, and it depicts the natural landscape of Tonle Sap Lake with the characteristics of "lake facies in both low and high water levels". Taking Kompong Luong Station and discharge controlling Prek Kdam Station of Tonle Sap Lake as represent stations, the responding correlations between water level - area (volume) relation and measured water levels are set up. The results show that the area and volume relation of Tonle Sap Lake forms a nonlinear one-to-one correspondence relationship with the water level of Kompong Luong station, but it forms a loop-like curve with the water level of Prek Kdam Station. One side of the loop-like curve is corresponding to the backflowing of Mekong River into Tonle Sap Lake in flood season, and the other side is corresponding to Tonle Sap Lake water outflowing to Mekong River after the flood season. On the basis of river-lake relationship, the correlation between measured water level of Prek Kdam Station and the area (volume) of Tonle Sap Lake under different periods and river-lake water level differences is constructed. The refined calculation results of water level - area (volume) of Tonle Sap Lake can provide scientific and technological support for the accurate prediction of flood control and drought resistance.