The tensile behavior of (Fe₅₀Mn₃₀Co₁₀Cr₁₀)_100-xSi_x (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 transformation- induced 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.