Abstract: Public Choice and Constitutional Economics are the academic basis of Buchanan's theory of limited government. The constitutional democracy theory is nuclear in his theories of limited government.Buchanan's theories of government pay attention to how to defend government against danger and inspire potential of the state.This paper has discussed academic basis of Buchanan's theories of the government:Government Failure, Constitutional Democracy,Competitive Federalism, Moral Order and etc.and then made a brief comment.