The　tensile　behavior　of　(Fe50Mn30Co10Cr10)100-xSix　(x=0　(Si0),　2　(Si2))　metastable　HEAs　prepared　by　selective　laser　melting　was　studied　at　cryogenic　temperatures.　The　results　demonstrate　that　the　addition　of　Si　leads　to　lattice　distortion　and　a　decrease　in　stacking　fault　energy,　especially　at　77　K,　which　significantly　promotes　transformationinduced　plasticity　(TRIP)　in　Si2　HEAs.　The　yield　strength,　tensile　strength,　and　ductility　of　Si2　HEAs　are　505.2　MPa,　1364.1　MPa,　and　19%,　which　are　43%,　53%　and　58%　higher　than　those　of　Si0　alloy,　respectively.　TRIP　is　the　main　deformation　mode,　in　addition　to　dislocation　slip,　and　plays　a　key　role　in　strengthening.　The　reinforced　and　continuously　sustained　TRIP　maintains　a　dynamic　strain　distribution　during　deformation.　Ultrahigh　strain　hardening　greatly　enhances　the　strength　and　ductility.