Abstract: According to the character of East Lake in Wuhan City,the dimentional diffusion model of water quality and its solution have been studied.The counting speed and accuracy have been improved by using the two-dimentional replacement method.The improved interpolating model is used in the definition of edge consistency values and initial values for differential equation.At the same time the digital elevation model of the lake bottom is formed.The space and attribute files in GIS are established through transformation on the basis of the formation of equal consistency line,thus completing auto-classification.