Ab　initio　Hartree-Fock　theory　at　the　aug-cc-pvtz　level　is　used　to　investigate　the　equilibrium　structures　and　isomerization　of　HSOF　system.　All　of　the　transition　states　have　been　calculated　and　confirmed　by　the　intrinsic　reaction　coordinate　(IRC).　Four　equilibrium　structures,　HSOF,　HOSF,　SO(H)F　and　OS(H)F,　are　predicted　in　this　paper.　Though　OSF2　has　been　observed　experimentally,　the　present　calculated　results　suggest　that　the　linear　form　isomer,　HOSF,　is　more　stable　than　OS(H)F　by　35.　kJ/mol.　The　linear　form　HSOF　and　the　branched　SO(H)F　isomer　are　more　unstable　and　the　computed　relative　energies　are　318.3　and　510.0　kJ/mol,　respectively　with　respect　to　HOSF　isomer　corrected　with　zero　point　vibrational　energy.