In digital earth based virtual environments representation of clouds from earth scale to small regional scale is characteristic but not addressed yet. Our methods integrate clouds of different scales and achieve seamless switch between them when view position changes. The paper uses an interactive physical based method to calculate density distribution of earth-scale clouds with initial conditions provided by inputting data graphs, and generates a more detailed cloud map using advecting textures approach, this cloud map is then used as the texture of earth-scale cloud. Based on the earth-scale cloud density and the cloud map, a metaball based method to generate high detailed cloud density distribution is proposed, with which we can get a result conformed to the density distribution of earth-scale clouds. A seamless integration frame is employed to make the switch between different scales smooth and seamless. Results of test on our digital earth platform prove our methods maintain a good consistence and smoothness among clouds of different scales.