Based on the Market Process and the Individualism Methodology of the Austrian School of Economics,the article tries to introduce the concept of Market Public Interest and compares it with the Invisible Hand principle of Adam·Smith. The article points out that the concept of Externality should be re－understood against the background of Market Public Interest.In fact,the market is an ocean of externalities.In the free market,consumers and entrepreneurs will reflect to the externalities, so the market public interest increased during this process.Therefore,the Externality itself is not a problem and doesn’t mean Market Failure, and actually, the blocking of people’s reflection to the externalities by themselves is the real problem.The Property Right is a concept of status, and adjusting continuously with the individual action.Compared with the concept of Market Public Interest,the article argues that Ronald Coase’s concept of Aggregate Social Product is a static concept and lacks practical methodology foundation.