Economics is a rapidly developing discipline. Although the basic theory has not changed much, there will be many new examples. Man Kun's Principles of Economics is an introductory textbook of economics, which is divided into two volumes, while the undergraduate textbook of economics generally uses macroeconomics and microeconomics, which is an intermediate textbook of economics. Most people think that it is the upper and lower volumes of Principles of Economics, but it is actually wrong. They are similar in content, but there are still differences in arrangement order and content depth.