The present invention provides a method for adding a secondary serving cell, an apparatus, a device, and a network system. The method includes: communicating, with each other to acquire a unified serial number of a random access preamble code, a unified serial number of a PRACH mask code, and a unified cell radio network temporary identifier of a terminal; scrambling the serial number of the random access preamble code and the serial number of the PRACH mask code, and then sending the serial number of the random access preamble code and the serial number of the PRACH mask code to the terminal; and determining, a time advance command TAC according to a random access request message that carries the random access preamble code, and sending the TAC to the terminal.