A topography-based dynamic critical arearainfall threshold model was developed for solving flood warning of the ungauged and small to middle-sized basin in this paper. The exponential equation model between dynamic critical arearainfall threshold and four main characteristic factors was established. The four main characteristic factors include basin area, channel slope, land use and soil type, which affect the flood generation processes primarily in small to middle-sized basins. Dynamic critical arearainfall threshold in the ungauged basin is calculated with the developed exponential equation model of the gauged basins and four main characteristic factors of the ungauged basin. Five small to middle sized basins in the subtropical monsoon climate region of eastern China were selected as the test basins, 〖JP2〗including Huangchuan Basin of Huaihe River, Tunxi and Yuliang basins of Qiantang River, Xitiaoxi and Nantiaoxi basins of Taihu Lake. Taking the warning flood as an example, dynamic critical arearainfall thresholds of Huangchuan, Yuliang, Xitiaoxi and Nantiaoxi basins were inversed with the long-term hydrological and meteorological data by the GMKHM hydrological distributed model. According to the developed critical threshold model, dynamic critical arearainfall threshold of Tunxi Basin was calculated 〖JP2〗based on the developed exponential equation model.〖JP〗 The topography-based dynamic critical arearainfall threshold was applied to flood warning verification of 35 representative flood events in Tunxi Basin. The results show that flood warning hit rate based on the topography-based dynamic critical arearainfall threshold is 91.4%， which is close to that on the basis of dynamic critical arearainfall threshold calculated with long-term hydrological and meteorological data in Tunxi Basin. The developed topography-based dynamic critical arearainfall threshold model has certain reference significance for similar flood warning of ungauged basins and flash flood warning.