In the field of communication technology, a method for invoking a Universal Service Interface (USI) and a USI system are provided. The schemes provide a user with a short-lived user ID for the application to interact with the USI system. The short-lived ID has a corresponding relation with the long-lived user ID and can be found according to the long-lived user ID regardless of whether the user is online or offline. The method and device can effectively ensure the security of USI invocation, and ensure that the application can initiate the USI service request even when the user is in an offline state.