The public domain in the Copyright Law refers to the domain of knowledge that is not protected by copyright, including noncopyrightable and copyrightable public domain formed based on public interests, works that have passed the copyright protection period, and works for which the copyright owner voluntarily waives the rights.Both labour theory of possession property and the interest balance theory contain the concept of public domain reservation.The public domain can help define the boundaries of copyright rights and achieve the public interest purposes of copyright law.Through a typology of cases, the way in which the public domain doctrine has been applied by parties and courts is summarised, and it is found that the public domain doctrine can be applied both as evidence to infer the facts of a case and as reasons to enhance the reasoning of a judgment.By unifying the content of the public domain and the principles of judicial review the purpose of the public domain doctrine guiding the judicial practical application of copyright law can be achieved.

copyright law; public domain; social public interest; public domain reservation