A traffic control method and system for a broadband user-network interface which connects subscriber terminals to a public network in an ATM exchange including a broadband-terminal equipment, a local exchange which fixedly assigns virtual path identifiers in accordance with traffic characteristics and processes the traffic received through the assigned virtual path identifiers and a virtual channel identifier, and a broadband-network termination disposed between the broadband-terminal equipment and the local exchange for modulating and demodulating a signal transmitted/received and outputs a modulated/demodulated signal. The broadband-network termination includes a connection control unit for analyzing call establishment request information from one of a plurality of subscriber terminals to thereby detect a corresponding traffic class, quality of service and address of destination, and controlling connection admission based upon detected information and simultaneously outputting transmission bandwidth information to thereby assign a virtual channel identifier; a generic flow control unit for analyzing a generic function control field in a cell header of a received cell generated from a call connected through the connection admission control unit to fairly use public media used by the plurality of subscriber terminals for minimizing cell transmission delay; a traffic control unit for monitoring whether the received cell indicative of the call violates traffic parameters described by the calling subscriber terminal and controlling a cell loss priority bit in a corresponding cell header to thereby execute cell transmission, cell shaping, and cell discarding.