Abstract: Radio frequency identification (RFID) is a critical technology which can realize the unique identification of objects through radio frequency signals. However, with the wide application of RFID technology, the number of tags is gradually increasing, and the demand for RFID system performance, especially the anti-collision capability, is also growing. Among the many demands, the anti-collision capability of the system is a widely considered application requirement. In this paper, the RFID system process and the traditional anti-collision strategy is briefly introduced. Then, the improved physical layer-based collision avoidance strategy is studied in detail. The improved anti-collision strategy is analyzed from four aspects: reader strategy, antenna size, channel and link, and tag size. Finally, the technical challenges in the current systems are summarized, and the future directions of the RFID system are prospected.