The flap rail track is controlled track and geometric characteristics of flap, and it’s also an important input conditions of aircraft flap control rail mechanism. A new design method of fowler flap rail track is proposed, which according to the motion rule of fowler flap，the movement of the flap is simplified to a conical surface around a certain point outside the wingtip approximately, then the simulate functions of CATIA V5 are used to design the fowler flap rail track. In the end , the example of Y12F is given to show the effectiveness of this method.