The　behavior　of　magnetic　and　structural　transitions　in　Y　substituted　MnCoGe　system　is　investigated　in　this　study.　Both　Mn　and　Ge　deficiencies　in　MnCoGe　phase　are　induced　by　a　single-site　Y　doping.　The　structural　transition　temperature　thus　shifts　to　lower　temperatures　and　creates　a　Curie　temperature　window　as　wide　as　86　K.　The　largest　magnetic　entropy　change　of　about　15.6　J/kg.K　and　refrigerant　capacity　of　about　132.8　J/kg　are　obtained　in　these　compounds.　The　samples　at　the　boundary　of　the　temperature　window　show　a　critical　phenomenon,　which　is　characterized　by　a　magnetostructural　transition　during　the　cooling　process　and　separate　magnetic　plus　structural　transitions　during　the　heating　process.　This　makes　it　possible　to　determine　the　contribution　from　the　magnetic　transition　to　the　total　entropy　change　in　magnetostructural　transition,　which　is　23-26%　in　present　system.