As a typical additive manufacturing technology, laser melting deposition (LMD) has been widely used to process high entropy alloy (HEA). However, deposited products usually have poor mechanical properties. In this study, deep cryogenic treatment (DCT) is proposed to enhance the mechanical performance of the laser melting deposited Fe50Mn30Co10Cr10 high entropy alloy. The tensile strength, hardness and strength-plasticity product of the HEA with 48hours of immersion by DCT processing were 901MPa, 286HV and 33.3GPa%, respectively. Compared to the as-deposited state, the HCP ε phase content and tensile strength of the DCTed sample increased by 2.2 times and 30.8%, respectively, while the average grain size decreased by 58.0%. Furthermore, the friction coefficient and wear rate of the DCTed samples reduced by 25.6% and 30.3%, respectively. The high temperature gradient soaking in liquid nitrogen induced dynamic recrystallization, refining the FCC γ grain structures in the HEA. Meanwhile, the samples contained more HCP ε phase due to the transformation-induced plasticity (TRIP) effect triggered by thermal stress. The results indicate that the effects of fine-grain strengthening and second-phase particle dispersion strengthening are the reasons for the excellent mechanical performance. DCT processing provides a simple and effective way for overcoming the strength-ductility trade-off in the additive manufactured Fe50Mn30Co10Cr10 HEA.