This application relates to the field of communications technologies, and discloses a network authentication triggering system, method and a related device. The method includes: receiving a first message from a terminal, where the first message carries first identity information and identifier information, the first identity information is encrypted identity information, and the identifier information is used to identify an encryption manner of the first identity information; and sending a second message to a first security function entity, where the second message is used to trigger authentication for the terminal, and the second message carries the identifier information. This application provides a solution of triggering an authentication process when identity information is encrypted.