Traditional calculation methods for designing the lowest navigable water level in reservoir areas mainly count discharge and calculate the inflow discharge according to guaranteed rate and water level in front of dams. However，these methods fail to consider the dispatching scheme of power stations. Taking Xiangjiaba Reservoir area in Jinsha River as an example，this paper analyzes problems that Xiangjiaba power station has different dispatching schemes，the water level difference in front of dams of high dam reservoir areas is large，and schemes using both guaranteed rate discharge and water level in front of dams are not suitable for the actual situation. Then，the paper studies the lowest navigable water level design. Based on the actual water level and discharge in front of dams，the paper calculates the lowest navigable water level in high dam reservoir areas and fluctuating backwater areas by four methods and compares the calculation results. The results show that the project scale in fluctuating backwater areas can be better determined by considering both water level and inflow discharge in Xiangjiaba Reservoir area，which is in line with the actual situation and can reduce cost.