The　Internet　of　Things　(IoT)　Technology　is　used　to　inspect　photovoltaic　(PV)　array　which　can　greatly　improve　the　monitoring,　performance　and　maintenance　of　the　PV　array.　In　order　to　efficiently　realize　the　remote　monitoring　of　PV　operating　environment,　an　on-line　monitoring　system　of　PV　array　based　on　IoT　is　designed　in　this　paper.　The　system　includes　data　acquisition,　data　gateway　and　PV　monitoring　centre　(PVMC)　website.　Firstly,　the　DSP-TMS320F28335　is　applied　to　collect　indicators　of　PV　array　using　sensors,　then　the　data　are　transmitted　to　data　gateway　through　ZigBee　network.　Secondly,　the　data　gateway　receives　the　data　from　data　acquisition　part,　obtains　geographic　information　via　GPS　module,　and　captures　the　scenes　around　PV　array　via　USB　camera,　then　uploads　them　to　PVMC　website.　Finally,　the　PVMC　website　based　on　Laravel　framework　receives　all　data　from　data　gateway　and　displays　them　with　abundant　charts.　Moreover,　a　fault　diagnosis　approach　for　PV　array　based　on　Extreme　Learning　Machine　(ELM)　is　applied　in　PVMC.　Once　fault　occurs,　a　user　alert　can　be　sent　via　E-mail.　The　designed　system　enables　users　to　browse　the　operating　conditions　of　PV　array　on　PVMC　website,　including　electrical,　environmental　parameters　and　video.　Experimental　results　show　that　the　presented　monitoring　system　can　efficiently　real-time　monitor　the　PV　array,　and　the　fault　diagnosis　approach　reaches　a　high　accuracy　of　97.5%.