The embodiment of the invention discloses a digital identity application system and method and an identity authentication system and method, and belongs to the technical field of digital identities. In this scheme, since the eID code is a digital identity which is signed and issued by an authoritative trusted platform and uniquely corresponds to each type of identity real-name information of the user, the obtained digital identity is authoritative enough and has a high security level, the reliability, security and effectiveness of the digital identity can be improved based on the characteristics of the eID technology, the risk that the digital identity is stolen, tampered and falsely used is reduced, and the identity information security of a user is ensured. According to the method, the user cost can be saved through a pure online mode, so that the application and authentication efficiency can be improved. The user can realize identity authentication of multiple certificates through one digital identity two-dimensional code, the purposes of multiple certificates in one and one-code multiple-certificate are realized, switching back and forth among multiple platforms is not needed,the operation is faster and more convenient, and the efficiency is higher.