The　grid-connected　system　of　single-pole　photovoltaic　inverter　is　taken　as　the　research　object,　the　concept　of　impedance　is　expanded,　and　a　passive　islanding　detection　method　based　on　the　common　coupling　point　(PCC)　comprehensive　impedance　is　proposed.　The　real-time　signals　of　voltage　and　current　are　extracted　by　fast　Fourier　transform.　By　identifying　the　change　state　of　the　comprehensive　impedance　at　the　PCC　point,　the　phenomenon　of　normal　and　isolated　island　is　distinguished.　The　simulation　results　show　that　the　isolated　island　detection　method　can　quickly　and　effectively　detect　the　isolated　island,　and　does　not　affect　the　output　power　quality　of　the　inverter.　©　2019,　Editorial　Board　of　Acta　Energiae　Solaris　Sinica.　All　right　reserved.