A cross-sectional shape generating method for the compact and offset bend double-S-inlet design of subsonic stealthy UAV is proposed according to curvature regulation. The inlet design procedure can quickly accomplish the surface composition of Double-S-inlet with complex conformal intake shape and complex bending style. Utilizing that method, six ducts are created and multi-parameters which include centerline curvature, area ratio and middle-cross-sectional shape are analyzed to studied the effects on duct perforce. Results indicate that the reverses at the top region of the second S part and the total pressure distortion arose by secondary flow should be considered carefully in the Serpentine inlet design procedure. Results also indicate that there are more complex flow structure in the Serpentine inlet compared to that in the S-duct inlet, and that the conventional design approach used in the S-duct inlet is still effective in the double-S-inlet design procedure.