Digital city and its sustainable development is the new vision on city civilization in the 21st century, which will greatly change the life conception, style and level of the people. The relationship of Digital City and sustainable development will affect the orientation and speed of worldwide economic development. The concepts and the relationship of Digital City and sustainable development are analyzed and their harmony and collision are studied in this paper. It suggests that Digital City is an important component of Digital Earth and a result of new technology revolution as well as the inherent necessity to the implementation of sustainable development. Digital City and sustainable development will be vested with new connotations with the development of the city.