In view of the lack of effective flow data for most rivers in the plain area, it is of great practical significance to study the calculation method of ecological water threshold for rivers in the plain area. In this paper, four representative ecological water quantity calculation methods and results, such as 7Q10 method, guarantee rate method, wet circumference method and ecological water level method based on Tennant improvement, are compared and analyzed. The applicability of the above methods is evaluated based on the principle of hydrological rhythm and ecological water level satisfaction. The results show that (1) In terms of the correspondence of hydrological rhythm, the ecological water level calculated by 7Q10 method, Q90 method and wetted perimeter method is a single specific value, which cannot reflect the natural change process of hydrological rhythm ; (2) In terms of ecological satisfaction, the 7Q10 method has the smallest satisfaction degree of multi-year average ecological water level ; (3) The hydrological rhythm simulation effect of the improved ecological water level method based on Tennant method is the best, and the ecological water level satisfaction is the highest. The research shows that among the four calculation methods selected, the improved ecological water level method based on Tennant method can better meet the principles of hydrological rhythm correspondence and ecological water level satisfaction compared with 7Q10 method, Q90 method and wet perimeter method, and has certain applicability to the calculation of river ecological water level (threshold) in plain area. The research results can provide a useful reference for the determination and management of river ecological water demand with lack of flow data in river network area of northern Jiangsu plain.