The　four-switch　Buck-Boost　converter　applied　to　the　fuel　cell　system　can　theoretically　achieve　higher　efficiency　under　the　traditional　two-mode　control.　But　in　fact,　in　the　process　of　transition　between　the　two　modes,　the　dynamic　performance　of　the　system　is　poor　due　to　the　influence　of　the　voltage　gain　blind　zone,　which　greatly　reduces　the　stability　of　the　converter.　In　high-power　applications　with　large　currents,　to　reduce　the　inductor　current　ripple　and　increase　the　power　density　of　the　converter,　the　interleaving　technology　is　usually　used.　In　this　paper,　a　smooth　mode　transition　strategy　of　the　four-phase　interleaved　four-switch　Buck-Boost　converter　is　proposed.　Firstly,　the　control　principle　of　the　converter　and　the　principle　of　four-phase　interleaving　are　analyzed,　and　the　basic　mathematical　relationship　of　the　converter　is　established.　Then,　the　voltage　gain　blind　zone　of　the　converter　is　analyzed　using　graphical　methods,　and　a　control　strategy　is　proposed　to　eliminate　the　blind　zone　and　realize　smooth　transition　based　on　the　traditional　three-mode　control　strategy.　In　the　dynamic　process,　the　duty　cycle　change　is　minimized,　and　the　inductor　ripple　current　is　also　optimized,　which　improves　the　efficiency　and　stability　of　the　converter.　Finally,　the　effectiveness　of　the　control　strategy　is　verified　by　experiments.　©　2021　IEEE.