Metal is one of the main environmental factors that affect the communication distance of ultra high frequency radio frequency identification（ UHF RFID） systems. For metal environment

most researches of domestic and foreign scholars are focused on anti-metal tag antenna

and they do not theoretically analyze on link of RFID system. Theoretically analyze on the forward link of the RFID system in metal environment

and obtains the relationship between the distance to the reader r change with the distance to metal surface Δr when the tag can work. The simulation result and experimental results are compared

differences between the theoretical calculation results and the experimental test results are analyzed in detail. When the result of Δr = 13 mm is obtained

the label can recover the normal communication distance.