Abstract: Tag collision in RFID system increases the time overhead and energy consumption of passive tags, reduces the recognition rate. An Uninterrupted anti-collision algorithm with ID-based Grouping (UIG) is proposed. Firstly, it separates tags into different groups resort to the company code and product code. Then, the algorithm generates two initial tag identification codes of each group by the collision information of products serial number. Finally, it identifies all tags via add or decrease 1 of the initial tags. Analysis of performance and the results of simulation show that the proposed algorithm improves the time complexity and communication complexity, the throughput is also greatly improved.