Prominent　problems,　including　the　high　investment　cost　and　limited　generation　revenue　of　offshore　wind　farms,　are　of　concern.　To　tackle　these　problems,　a　bi-level　model　is　proposed,　whose　upper　level　represents　the　offshore　wind　farm　optimization　for　the　target　of　maximizing　the　profit,　and　the　lower　level　represents　the　day-ahead　market　clearing　with　the　participation　of　an　offshore　wind　farm.　In　the　upper　level,　the　number,　type,　and　coordinates　of　wind　turbines　are　simultaneously　optimized　on　the　premise　of　the　determined　sea　area.　The　layout　of　an　offshore　wind　farm　in　irregular　sea　areas　can　be　obtained　by　constructing　specific　penalty　functions.　In　the　lower　level,　under　different　wind　conditions　and　load,　the　day-ahead　market　with　the　goal　of　maximizing　social　welfare　is　cleared,　and　the　cleared　wind　power　and　local　marginal　prices　of　an　offshore　wind　farm　are　provided　for　the　upper　level　model.　Finally,　the　optimal　number,　type,　and　coordinates　of　wind　turbines　are　obtained　by　solving　the　two-layer　model.　In　a　rectangular　planned　sea　area,　the　bi-level　optimization　model　is　successfully　applied.　The　test　results　show　that　when　27　wind　turbines　with　a　rated　capacity　of　6.45MW　are　placed　in　the　planned　sea　area,　the　annual　investment　profit　reaches　the　maximum　value　of　22.6　x　10(6)　euros.　When　the　optimized　layout　of　an　offshore　wind　farm　is　used,　the　power　deviation　of　67%　wind　turbines　caused　by　the　wake　effect　can　be　controlled　within　7%,　which　verifies　that　the　optimized　layout　plays　a　role　in　reducing　the　wake　effect.