One of peculiarities of stiffened panels (SP) design for aircraft composite wing with minimum weight is the necessity of taking into account possibility of different buckling failures with ultimate loads. Besides while designing SP it is necessary to take into account various modes of composite material failure including those originating from transverse shear stress influence. Composite SP design methods developed on the basis of equistability principal are offered in this work. Different variants of loading (including combined shear and compression loading) are taking into account. Analytical dependences of SP thickness vs load allowing to estimate different design concepts examined at an early stage of design and to compare different types of SP are obtained. Researches of SP element optimal reinforcement in case of stability strict restrictions have been performed on the basis of developed methods. Recommendations on several types of SP optimal reinforcement are given. Research results complement conclusions to which task of optimal reinforcement with static strength strict restrictions draw. Offered compressed composite SP design methods are modified taking into account traditional coefficients of reduction application which take into account possible local skin buckling. Analytical dependences allowing to define coefficients of reduction for composite compressed panels including those taking into account transverse shear stress influence have been obtained on the basis of geometrically nonlinear relationships of orthotropic panels. Stress distribution peculiarities in case of buckling relative to composite thick panels are shown. You can also find an estimation of bending stress influence. Recommendations on allowable stress choice for wing box upper SP optimal parameters definition in case of static strength and stability restrictions have been developed on the basis of performed researches.