Abstract: The UHF RFID tag is effected by the environment, especially liquid.Theory analyzing and test experiment, were used to study the effect of liquid on RFID tag.Changes of performance parameters were tested in liquid environment by using the RFID system test platform, and studied based on electromagnetic field simulation software HFSS Ansoft.The results show that the fluid near the RFID system can absorb electromagnetic wave, reduce the radiation efficiency of the tag antenna, and lead to impedance match of antenna gets changed.