Abstract: In microeconomics and macroeconomics, the prevailing definition of externality needs to be improved, and the understanding of the characteristics of public goods and public resources need to be corrected. In addition, the trade-off between marginal cost pricing and average cost pricing should be based on the market, the "contradiction" between I=S identity and I < S or I > S should be explained in accordance with theoretical logic, and the relevant analysis of investment multiplier can also be deepened.