The　structural　stability　of　high-entropy　alloys　(HEAs)　is　closely　related　to　their　mechanical　properties.　The　precise　control　of　the　component　content　is　a　key　step　toward　understanding　their　structural　stability　and　further　determining　their　mechanical　properties.　In　this　study,　first-principle　calculations　were　performed　to　investigate　the　effects　of　different　contents　of　each　component　on　the　structural　stability　and　mechanical　properties　of　Co-Cr-Fe-Ni　HEAs　based　on　the　supercell　model.　Co-Cr-Fe-Ni　HEAs　were　constructed　based　on　a　single　face-centered　cubic　(FCC)　solid　solution.　Elemental　components　have　a　clear　effect　on　their　structure　and　performance;　the　Cr　and　Fe　elements　have　an　obvious　effect　on　the　structural　stability　and　equilibrium　lattice　constant,　respectively.　The　Ni　elements　have　an　obvious　effect　on　stiffness.　The　Pugh　ratios　indicate　that　Cr　and　Ni　addition　may　increase　ductility,　whereas　Co　and　Fe　addition　may　decrease　it.　With　increasing　Co　and　Fe　contents　or　decreasing　Cr　and　Ni　contents,　the　structural　stability　and　stiffness　of　Co-Cr-Fe-Ni　HEAs　are　improved.　The　structural　stability　and　mechanical　properties　may　be　related　to　the　strength　of　the　metallic　bonding　and　covalent　bonding　inside　Co-Cr-Fe-Ni　HEAs,　which,　in　turn,　is　determined　by　the　change　in　element　content.　Our　results　provide　the　underlying　insights　needed　to　guide　the　optimization　of　Co-Cr-Fe-Ni　HEAs　with　excellent　mechanical　properties.