Abstract: The input queued switch fabric, because of its scalability, has been implemented in more and more high speed switches and routers. Existing scheduling algorithms attempt to get the maximum throughput at the expense of fairness. As the need for Quality of Service (QoS) becomes stronger, the efficient scheduling algorithm with guaranteed fairness for Input Queued (IQ) switch has become an urgent problem. In this paper a virtual service based fair scheduling algorithm with guaranteed fairness for IQ is proposed. Theoretical analysis and computer simulation show that this algorithm can provide better performance in respects of fairness and cell delay. With the same low communication cost as iSLIP and the same computing complexity as iLQF, this algorithm has better practicability.