In　order　to　implement　the　particle-in-cell　(PIG)　simulation　of　four　outer　magnetically　insulated　transmission　lines　(MITL)　of　Z-pinch　accelerator,　we　adopt　the　backward-going　transmission　line　voltage　wave　at　the　double　post-hole　convolute(DHPC)　travelling　in　the　outer　MITL　direction,　which　is　gained　in　circuit　simulation　to　model　the　part　from　DHPC　to　Z-pinch　load.　For　the　purpose　of　enhancing　the　accuracy　of　equivalent　circuit　model　of　DHPC　and　Z-pinch　load,　the　backward-going　transmission　line　voltage　wave　that　is　computed　by　circuit　simulation　is　rescaled　by　PIG　simulation.　The　insulator　voltage　and　current　waves　that　are　obtained　in　the　PIG　simulation　of　four　outer　MITLs　of　PBFA　Z　can　match　the　electrical　measurements　better　than　those　obtained　by　the　circuit　simulation.　Moreover,　the　influence　of　Z-pinch　load　implosion　on　the　process　of　pulsed　power　coupling　in　the　outer　MILT　is　analyzed　and　explained.