A limited deflection routing algorithm based on burst loss threshold for optical burst switching(OBS) network is proposed.It drops some high priority deflected bursts to provide QoS for low priority non-deflected bursts.When a deflected high priority burst arrives at a core node which has not any available channels,this node uses threshold check function to decide whether to drop or to preempt the resource of low priority non-deflected bursts on deflected route.Simulation results show that the proposed algorithm can efficiently prevent deflected burst from contending with non-deflected burst on deflection route,and effectively improve the burst loss performance of entire networks.