Abstract: Water resources are scarce and ecological environment is fragile in the arid regions of northwest China. How to scientifically deal with the relationship between production water and ecological water has always been one of the hotspot and difficult issues in the field of water resources development and utilization in northwest arid areas. However, there are few quantitative studies on the relationship between the ecological water conveyance from the middle and upper reaches of the basin to the downstream terminal lake (wetland) and the area of the terminal lake (wetland). In this paper, Qingtu Lake, the terminal lake of the Shiyang River Basin in Gansu Province, is taken as an example. A coupled model of surface water and groundwater is established using GSFLOW software, among which, LAK module and SFR2 module are used to treat the lake and water channel, respectively. Based on this, the changes of surface area of the Qingtu Lake under different ecological water conveyance schemes are predicted. The appropriate range of ecological water conveyance to the Qingtu Lake is determined. The results show that the current ecological water conveyance of 3100×10⁴ m³/a can ensure the highest water level of Qingtu Lake of 1212.23 m (the average water level of 1211.68 m) and the corresponding water surface area of 16.27 km². The relationship between ecological water conveyance and water surface area is as follow. When the water delivery is in the range of 2000×10⁴−3700×10⁴ m³/a, the water surface area increases obviously and the area change rate is relatively stable with the increase of water conveyance; when the water delivery is in the range of 3700×10⁴−4500×10⁴ m³/a, the increasing water surface area gradually decreases and the area change rate gradually decreases with the increasing water conveyance; and when the water conveyance is more than 4500×10⁴ m³/a, the increase of water surface area with the increasing ecological water conveyance is very small, especially when the ecological water conveyance is more than 5500×10⁴ m³/a, the change rate of water surface area tends to 0. Considering the demand for maintaining the current water surface area of the Qingtu Lake and the benefits of ecological water conveyance, the ecological water conveyance volume from the Hongyashan reservoir to the Qingtu lake should be in range of 3100×10⁴−4500×10⁴ m³/a. The results are of certain reference value in determining the local ecological water demand and maintaining the coordinated and sustainable development of local ecology, economy and society.