Abstract: The processing of personal information on the platform is a private law issue, and public law protection needs to be demonstrated. The protection of personal information by public law should not only be based on functionalism, but also on normative considerations. In terms of scenario construction, personal information may be related to public interests, and platform may also engage in state action due to the performance of public functions, public law can only be involved based on public interests maintenance and targeting platform state action. In terms of protection path, when protecting personal information based on public interests, administrative agency can protect personal information by means of prior permission, in-process supervision, and post processing. Individuals and procuratorate can also file administrative lawsuits to urge administrative agency to perform their protection responsibilities. When protecting personal information against platform state action, public law can be applied directly or indirectly to platform behavior and damage relief. Public law intervention in personal information protection should establish a reasonable limit. The protection of personal information by public law based on public interests should be based on the premise that the platform violates public law obligations or violates private law obligations to a certain extent. When the public law protects personal information for state action of the platform, it should only apply public law to quasi administrative action of the platform.