Tag collision occurs when a reader attempts to identify a large number of tags simultaneously, which reduces the identification efficiency of RFID systems. The dynamic slots collision tracking tree algorithm (DSCTTA) can reduce the prefix overhead and iteration overhead by using time-divided responding scheme, however, this mechanism generates a lot of idle time slot. An improved dynamic slots collision tracking tree anti-collision algorithm (IDSCTTA) is presented in this paper. The proposed IDSCTTA can combine the DSCTTA and the bits change method (BCM) to inherit merits of the DSCTTA. It can also suppress the generation of idle slots. The simulation results show that, the IDSCTTA can effectively reduce the identification delay and improve the slot efficiency.