In order to overcome shortcomings of traditional indoor positioning technology and meet a large number of the current indoor positioning needs

design a kind of radio frequency identification（ RFID） indoor positioning system based on phase difference ranging

which is mainly composed of a RFID reader

electronic tags and a microprocessor module. 3 electronic tags are fixed at particular positions as beacon nodes

and a RFID reader can transmit and receive ultra high frequency signals as mobile node. The STM32 calculates the corresponding distance between two points according to the phase difference

and ultimately determines the location information of the reader through the improved trilateration localization algorithm. The system is designed and test in laboratory

the results show that the system can perfectly achieve the positioning function

and positioning precision reaches cm level

that can meet the application needs of many fields.