In order to reduce the total time of reader identification in RFID system, a new packet DFSA algorithm is proposed to reduce the intra group efficiency of packet DFSA algorithm. The reader sets a dynamic grouping factor by analyzing the recognition results in each frame, the tag generates its own characteristic value according to the chaos pseudo-random number, and then compares it with the grouping factor value to select whether to respond at the current frame. Matlab simulation shows that the system efficiency of the new algorithm is stable and the number of time slots needed for identification is reduced. When the number of tags to be identified is less than 300, the recognition time of DFSA and packet DFSA is reduced by 11.7% ~ 16.1%; when the number of tags to be identified is more than 1000, the recognition time is reduced by 48.8% and 17.14% respectively compared with DFSA and packet DFSA.