In a packet-switched network, latency is not avoidable and its characteristic always depends on the type of traffic flows and operating conditions. These affect the kind of services that the network can support as well as the Quality of Service (QoS) that the system can provide. To provide a fair service for users is always the main concern for any operators as well as service providers. A fair Delay-Differentiable queueing algorithm with QoS support called Delay-Differentiable Fair Queueing (D²FQ) is proposed. In the proposed algorithm, an additional delay-slot is used to re-order the departure order of flows according to its delay weight. D²FQ can also protect the honest flows in delay and throughput when a node is attacked by Defense of Service(DoS) and the overall computation of the proposed D²FQ is shown to be O(1). Algorithm analysis and simulation result are presented and the performance of D²FQ is evaluated.