This paper analyses ecological environment in the Yellow River Delta by applying ecotone theory and puts forward a formula of environment potential index(E) to measure environmental quality. Then, the formula is used to do evaluation and pre-warning of present ecological environment in the Yellow River Delta.After calculating E Values of Dongying's west City, East City and 92 rural and town regions, The evaluation. result shows that the general environmental quality is good at present and there is still mor...