Abstract:

Market structure and social welfare are the focus of anti-trust policy. The existing research paid more attention to the determining of market structure， while the study on how the change of market structure will influence social welfare is still lacking. Based on Armstrong's work， a new platform model is established that is able to analyze and compare the social welfare under different market structures. The results show that although a decentralized market structure and competition can reduce the platform's ability to charge monopoly price， the effect of the competition is limited by factors like user stickiness and cross externalities. At the same time， the cross externality loss caused by the decentralized market structure also has a negative impact on social welfare. Under the simultaneous effect of these two factors， the decentralized market structure and competition will decrease social welfare， not increase. As a result， a structuralist antitrust system is not applicable in the platform economy. Under a centralized market structure， if the government can effectively control the monopoly power of the platform， such as banning monopoly acts and reducing platform prices， the optimization of social welfare can be realized. Therefore， the anti-trust policy of the platform economy should not focus too much on the market structure， but on improving social welfare by supervising the behavior and price of platforms.

Key words: platform economy, market structure, antitrust, social welfare