According　to　the　theoretical　and　practical　experience,　the　affected　areas　of　destruction　soil　under　the　foundation　is　closer　to　circular　slip　surface,　further　less　than　the　logarithmic　spiral　of　traditional　theory.　This　article　assumed　that　the　center　of　series　the　arc-shaped　sliding　surface　were　in　the　bottom,　then　according　to　the　minimum　security　and　stability　coefficient,　the　determined　center　of　a　circle　at　the　edge　of　the　base　of　the　foundation　is　the　most　dangerous　slip　surface　when　the　overall　instability　of　the　foundation.　With　limit　equilibrium　method,　the　author　deduce　a　new　theory　formula　for　calculating　the　bearing　capacity　of　strip　foundation.　And　it　is　taken　to　compare　with　several　existing　calculation　methods　of　foundation　bearing　capacity　to　evaluate　it　the　legitimacy　and　applicability　of　engineering　practice.