With the demand of renewable energy due to the pressure from environmental pollution and global warming, the wind industry has been growing rapidly over the past decades during which the offshore wind innovation is becoming more and more attractive because of vast offshore wind resources.In this paper, a novel tapered-column semi-submersible floating foundation with economical mooring system is developed to support 6MW wind turbine in South China Sea. The coupled aero-hydro-servo-structural analysis is done in GH-Bladed software to obtain the global dynamic response of the whole floating wind turbine. By combining the derived wind loads with the wave and current induced loads, the global performances of the foundation and attached mooring system under both extreme conditions and normal operation conditions are analyzed in AQWA software. The result reveals that the floating foundation complies with the design standard and meets requirements of wind turbine.This novel patent-pending floating foundation with tapered columns is proved as a successful design with high material efficiency and good seakeeping performance. Also a reliable and efficient design methodology of floating foundation based on optimal cost is provided in this paper which can be used as design reference of floating foundations.Copyright © 2015 by ASME