The　pole-changing　permanent　magnet　(PCPM)　machine　directly　changes　the　polarity　of　low　coercivity　permanent　magnet　material　for　pole-changing　or　pole-changing　flux　weakening　speed　regulation.　It　not　only　possesses　the　advantages　of　wide　speed　regulation　as　the　pole-changing　induction　motor,　but　also　featured　by　the　characteristics　of　high　efficiency　and　high　power　factor　of　permanent　magnet　machine.　Consequently,　it　is　promising　for　some　applications　with　wide　speed　and　high　efficiency　range.　On　the　basis　of　investigating　the　pole-changing　speed-regulation　principle　and　operating　conditions　of　the　PCPM　machine,　the　reviewed　machines　can　be　divided　into　rotor-PM　type　and　stator-PM　type　according　to　the　PM　position.　This　paper　analyzed　and　compared　the　structure　characteristics　of　the　existing　PCPM　machines,　and　summarized　their　common　regularity　and　individual　characteristics.　Meantime,　the　key　common　technologies　of　the　PCPM　machines　were　carried　out,　concerning　mainly　about　the　pole-changing　winding　design,　analysis　methods　and　pole　protection　schemes　as　well　as　control　technologies.　Finally,　the　future　trends　of　the　machine　systems　are　prospected.　©　2021　Chin.　Soc.　for　Elec.　Eng.