Aiming　at　the　problem　of　high　switching　frequency　and　zero-crossing　distortion　in　the　Boost-PFC(power　factor　correction)　circuit　near　the　zero-crossing　of　AC　input　voltage　in　critical　conduction　mode,　which　leads　to　the　increase　of　circuit　switching　loss　and　total　harmonic　distortion,　on　the　basis　of　constant　on-time　control,　a　current　control　strategy　of　frequency　foldback　is　proposed.　By　switching　the　circuit　from　the　critical　working　mode　to　the　discontinuous　working　mode　near　the　AC　input　voltage　zero　crossing,　the　switching　frequency　of　the　circuit　near　the　AC　input　voltage　zero　crossing　was　reduced,　and　the　efficiency　of　the　converter　was　improved.　The　switching　tube　conduction　time　of　the　circuit　was　increased　when　the　AC　input　voltage　was　near　zero　crossing,　and　the　inductive　energy　storage　was　increased,　so　that　the　diode　can　still　conduct　near　the　AC　input　zero　crossing　and　the　zero　crossing　distortion　was　improved.　The　simulation　and　experimental　results　show　that　the　circuit　can　reduce　the　working　frequency　and　increase　the　on　time　by　switching　to　discontinuous　mode　when　the　AC　input　voltage　crosses　zero.　The　efficiency　of　the　Boost-PFC　circuit　is　improved,　and　the　total　harmonic　distortion　of　the　circuit　is　reduced.　©　2022,　Harbin　University　of　Science　and　Technology　Publication.　All　right　reserved.