This paper is going to present a new algorithm called "PP" (a RFID anti-collision algorithm based on pipeline and pre-detecting mechanism) to solve the problem of collisions among the tags in RFID system. This algorithm provides a hardware architecture consisting of two antennas: a pre-detection antenna for pre-detecting and a reading antenna for tag reading, the two processes of which will work respectively and concurrently based on pipeline system. Compared with other related researches, this algorithm that avoids the waste of time in the process of pre-detecting and free from the limitation-the ratio of the length of detection slot to reading slot-will contribute to a non-stop reading operation. Our simulation illuminates that the proposed PP algorithm outperforms the existing ones in efficiency, stability and the leakage rate of tags.