Except that the man cannot understand natural and ecological laws, the reason for causingenvironmental pollution and ecological destruction, from economic point of view, is mainly that the man doesnt fully weigh the relationship between economic development and environmental protection, is that the man only considers short-termed and direct economic benefit, however, neglects the long-termed effect economic development brings about on nature and society.Environmental impact assessment system plays positive role on preventing and controlling environmental impact and ecological destruction from its birthday. It makes policy-makers fully know environmental impacts and ecological destructions which decisions may cause before making decisions,and take necessary measures in order to mitigate negative effects decisions will bring about on environment.