In many RFID applications, we conduct a RFID reader network to monitor a large number of tagged items. We also want to utilize this network to trace un-tagged items. In this paper, we propose ARNS-Adaptive RFID Network Scheduling scheme for device-free tracking. In particular, we firstly deploy a set of readers and reference tags into the monitored area. Then, we divide the tags within the read region of a reader into two groups, one in reader-to-reader collision area while the other not. We monitor the area by normal sampling model in which we need two phases to separately query the two groups. When an un-tagged target appears in the monitored area, we adopt tracking sampling model. In tracking sampling mode, the reader who detects the tags' frequency variations will adaptively query all tags in its read range to obtain the target's full trace. Meanwhile, we fill the missing path using shortest-path algorithm to recovery the trajectory. Experimental results show that ARNS achieves high tracking accuracy for certain applications.