A radio frequency identification (RFID) system employs multiple band transmission to prevent signal collision. The system includes a plurality of RFID tag groups and at least one RFID reader. Each RFID tag group includes at least one RFID tag. The RFID tags of the same RFID tag group are operated for radio frequency transmission in the same transmission frequency band, and those of different RFID tag groups are operated for radio frequency transmission in different transmission frequency bands. When the RFID reader simultaneously receives radio frequency signals issued from RFID tags of different RFID tag groups, since they are transmitted in different transmission frequency bands, signal collision among the RFID tags of the RFID tag groups can be avoided.