A first correspondence table in a terminal device stores a correspondence between an identifier of a process running on the terminal device and an identifier of a data stream created by the process, a second correspondence table stores a second correspondence between an identifier of an application and an identifier of a process created by the application. The terminal device receives an identifier, sent by a network security device, of a first data stream. The terminal device can find, in the first correspondence table, a first record storing the identifier of the first data stream to obtain an identifier of a process. The terminal device can find in the second correspondence table, a second record storing the identifier of the process in the first record to obtain an identifier of an application from the second record. The identifier of the application is then sent to the network security device.