The　6p　orbit　coupling　of　bismuth　ions　and　the　magnetism　of　iron　ions　endow　bismuth-iron　compounds　with　magnetic,　optical　and　electrical　properties.　In　this　paper,　non-rare-earth　bismuth-iron　crystals,　KBa8Fe12(Bi6−xFex)O38　(x　=　0.2,　1.1,　2.0,　2.9,　and　3.8),　with　a　large　magnetocaloric　effect　were　prepared　by　a　hydrothermal　method.　The　structure-function　relationship　is　discussed.　With　the　increase　of　the　Fe　content,　the　lattice　parameters　and　unit　cell　volume　decrease,　while　the　magnetization　intensity　shows　an　increase　on　the　whole　and　a　fluctuation　at　the　same　time.　The　increase　of　the　Fe　content　can　improve　the　magnetocaloric　effect.　Importantly,　the　maximum　magnetic　entropy　change　(ΔSM)　of　KBa8Fe12(Bi4.9Fe1.1)O38　is　as　high　as　1.54　J　kg−1　K−1　at　the　low　temperature　of　2　K.　©　2023　The　Royal　Society　of　Chemistry.