The digital earth model is composed of three parts： digital frame model, digital elevation model, and digital earth-unit model. The question of building virtual earth in science mainly includes two sections： building the digital earth model and applying and developing modeling information effectively. The five characteristics of virtual earth and the key technologies for building digital earth model are introduced. This paper also discusses the seven engineering fields in which the digital terrain model is widely used. In the process of constructing ,researching, and developing the digital earth model, attention should be paid to environment pollution, plough land decrease, waterlogging and east-west regional variances, which have influence on China´s na-tional economic construction.