Sustainable development is not only a key measurement to evaluate the potential national power; it also can be used as an indicator to estimate the balance of regional economics from time to time. Therefore, sustainable development has become a significant studying subject for many scholars and experts who concern economic development. In the beginning of this assay, the efforts form Union Nation of forming and promoting sustainable development will be described, and then some supportive theories proposed by famous economists will also be bought up to demonstrate sustainable development are focusing on three key elements, which are economic development, social development and environmental protection. In the matter of fact, those theories are more or less known and applied by many economists, especially the limitations of the environment and nature resources. This assay will use economic development, social development and environmental protection, three key elements of sustainable development, to draw an equilateral triangle to highlight the value and balance of each element. In order words, it manifests the equal development among these three elements can actually enhance the national power and maintain the balance of regional economics. In the meantime, the regional economic development in Mainland China will have a great chance to face the challenge to build up the sustainable development ability no matter how the resources can be integrated. Especially under the rapidly economic growth within near 15 years (1990-2005), Mainland China need to be more careful on handling and remaining development balance among economics, society and environment from time to time. If the equilateral triangle of sustainable development can be successfully established, Mainland China will enable to take the benefits and advantages of the development outcomes for centuries.