The aim of this paper is to analyze water stable isotopes(δD and δ¹⁸O)in Lake Hulun Basin, and to explore the indicative function of stable isotopes in hydrological cycle in this region. The analytical results of lake water, river water and well water around Lake Hulun indicate that there are temporal variations of stable isotopes in lake and river water and spatial variations in river water along the flow path. Furthermore, the relationship between δ¹⁸O and δD in lake water, river water and groundwater in Lake Hulun Basin shows the crossing points of lake and river water are located in the lower right of local meteoric water line, suggesting lake water and river water have suffered from evaporation. However, the crossing points of well water are located closely to the local meteoric water line except southwestern area (W1) around the lake, indicating all groundwater except W1 reflects a precipitation origin, and the weird high isotope values in W1 may have connections to the lake water and well water. Using the relationship between stable isotopic ratio in residual water and residual water proportion with consideration of the effect of temperature and humidity, the proportions of modern lake water and river water after evaporation are calculated as 0.85-0.96 for river water, and 0.71-0.77 for lake water. Obviously, the extent of lake water evaporation is greater than that of river water, with 4%-15% water loss for rivers and 23%-29% water loss for the lake. In addition, the annual lake water evaporation was calculated based on isotopic mass balance method, the low relative error (5.4%) compared with measured data indicates this model is appropriate to calculate water evaporation for Lake Hulun. Using stable isotope (δD and δ¹⁸O) is an essential method to study on hydrological cycle in a basin, thus stable isotope still has a wide application space in hydrological cycle in Lake Hulun Basin.