An　optimal　design　method　combining　the　system　simulation　technology　and　the　multi-object　decision　technology,　which　can　be　used　for　optimum　design　of　piled　rafts,　is　presented.　The　objective　function　for　the　optimization　is　defined　as　the　volume　of　materials　of　piled　rafts,　while　the　variables　are　raft　thickness,　pile　length,　pile　spacing　and　pile　location.　First　using　orthogonal　test　to　optimize　system　input　scheme,　then　applying　3DFEM　to　calculate　system　output,　at　last　the　multi-object　decision　technology　is　adopted　to　evaluate　output　and　acquire　optimal　solution.　The　validity　and　effectiveness　of　the　proposed　method　is　examined　by　a　numerical　example.