Provided is a method and system for providing a QoS in a broadband convergence network deploying a mobile IP. In the method, a service and policy is defined at a first network design stage for guaranteeing the QoS of the broadband convergence network. QoS parameters corresponding to the defined service and policy are reflected in a DSCP field corresponding to the defined service. The DSCP field and the QoS parameters are applied to an access router in a management network. Accordingly, the QoS can be guaranteed to be suitable for the service and policy and a seamless handover guaranteeing the QoS can be provided.