The　suction　caisson　is　a　large　top-closed　cylindrical　steel　structure　in　diameter,　short　in　length　and　much　thinner　in　skirt　wall　thickness.　The　total　resistance　of　the　suction　caisson　during　installation　consists　of　the　tip　resistance　and　the　skirt　wall　friction.　However,　since　the　thickness　of　the　skirt　wall　is　very　small,　the　skirt　wall　friction　may　produce　additional　vertical　stress　and　shear　stress　in　soil　at　the　skirt　tip　level,　and　this　additional　vertical　stress　and　shear　stress　will　contribute　to　the　increase　in　the　skirt　tip　resistance.　At　the　same　time,　seepage　induced　by　suction　also　causes　the　tip　resistance　to　reduce　significantly.　A　modified　slip-line　field　is　proposed　in　this　study　estimating　the　tip　resistance　in　terms　of　the　slip-line　theory.　The　expression　obtaining　the　minimum　suction　to　install　the　suction　caisson　is　also　proposed　in　terms　of　the　force　equilibrium.　In　addition,　the　critical　suction　is　determined　based　on　the　mechanism　of　sand　piping.　Thus,　the　maximum　penetration　depth　of　the　suction　caisson　can　be　reached　when　the　critical　suction　equals　the　minimum　suction.　Results　from　calculations　of　the　minimum　suction　and　the　maximum　penetration　depth　have　been　proved　to　be　in　a　good　agreement　with　the　measured　data.　©　2017,　Korean　Society　of　Civil　Engineers.