The invention provides a method for low-correlation one-way cross-domain identity authentication based on private key. The method comprises the following steps: a user registers a user name in a common ID server and the system allocates a common ID to the user if the registration is successful; the user logins to the common ID server to acquire the authenticated ID; the user clicks the link of a Website in the common ID server and the common ID server transfers the common ID of the user and a relevant key to the Website; the Website receives the parameters transferred from the common ID server, if determining the first visit, allocates the user name to the user by use of the acquired two parameters (i.e. common ID and key) and calls a log-in module to succeed in the identity authentication; and if determining the second visit, the Website calls the log-in module to succeed in the identity authentication by use of the acquired two parameters (i.e. common ID and key). The method is applied to the log-in procedure bound to the mobile telephone number of the user and the multiple internet application names of the user in the mobile internet, and has the advantages of good privacy property, easy use, convenience for network management and strong applicability.