In order to support the scheme demonstration of widebody jetliner engine and the further research on geared turbofan, this paper focus on the Fan Drive Gear System conceptual design. The FDGS of star gear configuration consists of five branches which are of herringbone gears. It also has several features as follow. The sun gear is floating while using spine to transmit torque. The planetary gears are of integrated gear/bearing using single row spherical roller bearing. The ring gears are flexible mounted using friction to transmit torque. With the conceptual design, several technical difficulties are analyzed for further research such as transmission efficiency, load sharing, mounting structures, tooth surface modification and system dynamic.