A method and apparatus for a switch operation of a downstream terminal platform for Internet Protocol (IP) data transmission using a legacy transmission system in a Hybrid Fiber Coax (HFC) network is provided. The downstream terminal platform includes: a Radio Frequency (RF) transmitter to distribute and combine a signal transceived by an HFC network; a broadband downstream receiver to process a broadband signal received by the RF transmitter; a cable modem (CM) to process data received or transmitted by the RF transmitter; an IP layer switch to transmit data to a corresponding Customer Premises Equipment (CPE), the data being received from the broadband downstream receiver to the CPE, or to enable user data received from the CPE to be transmitted to a headend using the CM; and a subscriber controller to control the downstream terminal platform.