A radio frequency identification (RFID) tag access method and a circuit applied to an RFID tag to determine whether to respond to a command sent by a reader are provided. According to the access method, an extra reference value is used for adjusting a parameter or a count value, so as to increase or decrease the probability of generating a condition matching with a command sent by the reader. Therefore, the probability of the tag being accessed is adjusted, and the tag carrying urgent information shall be accessed prior to the tag without urgent information.