Abstract： Aimed at the RFID (radio frequency identification) collision problem caused by multiple access of shared channel, this paper proposed two RFID adaptive N tree anticollision algorithms based on bitmap construction, single frame bitmap track N tree algorithm (SFBTNA) and multiframe bitmap track N tree algorithm(MFBTNA). First of all, the two methods take advantage of the maximum likelihood tag numbers estimation method (MLBE) that can effectively estimate the number of tags. Secondly, based on the MLBE, it put forward the probe method construct bitmap. The SFBTNA adaptively adjusts the optimization value of N and builds N trees on one frame based on bitmap. The MFBTNA adaptively adjusts optimization value of N and builds N trees frame by frame. At the same time, the SFBTNA and MFBTNA identify the subtrees using collision track tree algorithm (CT). The combination of bitmap and CT greatly reduces the impact of collision time slot. Theoretical analysis and simulation experiments show that the performance of the two algorithms is higher than that of the other existing anticollision algorithms.