The large civil aircraft require a corresponding fairing for the mechanism of trailing edge flap which extends out of the wing surface and brings the aerodynamic losses. The dimension and figure of fairing has a great effect on the aerodynamic characteristics of the aircraft. When designing the fairing, the fairing shape design disciplines should be complied with strictly, in order to make the drag during high-speed cruise as small as possible. In the basis of consulting relevant literature and a large number of fairing pictures, by using of the NURBS method in the computer-aided design(CAD),a set of detailed design method of a fairing shape of tracked flaps for large civil aircrafts is formulated. As aresult of this method, the fairing can package mechanism, reduce aerodynamic losses, at the same time it can also shorten fairing design period.