Magnetic　refrigeration　based　on　the　magnetocaloric　effect　offers　a　potential　energy　saving,　atmosphere　friendly　way　to　replace　vapor-compression　refrigeration.　In　this　work,　Mn1.2Fe0.8P0.74Ge0.26-xSex　(x=0,　0.005,　0.01,　0.015,　0.02,　0.03)　compounds　were　prepared　by　mechanical　milling　and　subsequent　spark　plasma　sintering　(SPS)　technique,　their　crystal　structures,　phase　transition　process　and　magnetocaloric　properties　were　investigated　by　XRD,　DSC,　VSM　and　direct　measurement　equipment　of　magnetocaloric　effect.　The　results　show　that　the　Mn1.2Fe0.8P0.74Ge0.26-.xSex　compounds　possess　a　hexagonal　Fe2P-type　crystal　structure.　With　increasing　Se　concentration,　the　lattice　parameters　a　and　c　change　significantly.　It　causes　c/a　ratio　decreases　firstly,　keeps　unchanging　and　followed　by　increasing　again.　And　the　Curie　temperature　(T-c)　of　the　compounds　is　increased　with　the　decrease　of　the　c/a　ratio.　Either　applied　magnetic　field　or　temperature　change　can　induce　the　magnetic　transformation　between　the　paramagnetic　phase　and　ferromagnetic　phase.　Low　substitution　of　Se　for　Ge　(x　＜=　0.015)　in　the　Mn1.2Fe0.8P0.74Ge0.26-xSex　compounds　leads　to　higher　T-c,　narrower　temperature　range　of　the　two-phase　coexistence　(Delta　T-coex)　and　larger　adiabatic　temperature　change　(Delta　T-ad),　in　addition　the　thermal　hysteresis　(Delta　T-hys)　and　entropy　change　(Delta　S-DSC)　remain　almost　unaffected.　0.01　Se　substitution　leads　to　5.6　K　increase　in　T-c,10.6%　decrease　in　Delta　T-coex,　and　10%　increase　in　Delta　T-ad.　With　a　further　increase　in　Se　content,　magnetocaloric　properties　of　compound　decrease.