A　contactless　testing　approach　is　proposed　to　evaluate　the　parasitic　capacitance　of　ultra-high　frequency(UHF)　radio　frequency　identification　(RFID)　tag.　The　parasitic　capacitance　introduced　when　assembling　the　UHF　RFID　tag　chip　to　the　antenna　results　in　performance　deviation　of　the　tag.　This　parasitic　capacitance　affects　the　accuracy　of　tag　simulation　design　and　leads　to　the　detuning　of　the　RFID　tag.　This　paper　presents　the　analysis　of　parasitic　capacitance　through　theoretical　derivation　and　experimental　investigations.　The　method　is　established　based　on　the　equivalent　circuit　model　of　the　UHF　RFID　tag　and　the　expression　of　the　parasitic　capacitance.　The　measured　results　show　that　the　simulated　resonance　frequency,　taking　into　account　the　parasitic　capacitance,　closely　matches　the　measured　resonance　frequency.　This　study　can　provide　a　valuable　reference　for　the　good　design　of　the　UHF　RFID　tag.　　©　2023　IEEE.