Abstract: This paper presents the model of positioning system based on ratio frequency identification (RFID).Depending on geometry dilution of precision(GDOP),relationship between positioning precision and the number and arrangement of readers is discussed;arrangement strategy in real time location system (RTLS) is derived.The simulation results show that precision of location is improved with the increasing number of readers.When ranging error is 1.5 meters and the number of readers is 5,mathematical expectation of location error is 1.7262 meters,which satisfies the system requirement.