Abstract: To increase the whole strength and stiffness of the composite wing and to lower the manufacturing cost, the main component of the wing is employed with stitched technique. Intercostal is made from web and flanges, and is tailored from a whole knitted stitched laminate plate. Intercostal horizontal and vertical flanges are stitched on the skin and stringer blade respectfully; stringer flanges are stitched on the skin; then they can be integrated into structure by RTM. Direction of applied tension is on the intercostal web. There is shear stress between intercostal horizontal flanges and skin, causing slip delamination. There is tension stress between intercostal vertical flange and stringer blade, causing tensile delamination. Using a mixed 2D/3D FE model to the analysis gives the interface stress distribution among the intercostal, skin and stringer blade; the correctness of the analysis and calculation is also proved by test.