Abstract: The river fractal features can reflect the features of river systems,and the fractal dimension is an important variable that can reflect the fractal features. So there is certain relation between the river fractal dimensions and the river floods. By taking the middle and lower courses of the Yangtze River as an example,this paper calculates its fractal dimensions and analyzes its fractal features by grid-covered analysis,and tries to indicate the relationship between the river fractal dimensions and the river floods through the analysis. The results show that,the higher the river course fractal dimension,the lower the river network fractal dimension,the higher the possibility that flood-happens.