Abstract: An improved basic mechanical hypothesis was proposed toaccount for the mechanical behavior of grid stiffened composite panels.Withsuch hypothesis, a new smeared stiffener approach was developed toeffectively take into consideration the stiffener-skin interaction effects.The parametrized representation of grid unit cell was described, and thecorresponding mechanical model was estabilished. Such generalized model canbe used for global buckling analysis of grid-stiffened structures withdifferent types of grid layouts. Therefore, it is very useful for aerospacestructural design. Using Rayleigh-Ritz method combined with the developedsmeared stiffener approach, the eigen function for the globalbuckling load of grid stiffened panels was derived. Finally, various testexamples with different grid patterns were analyzed and the results werecompared with those obtained with existing methods. It is shown that the developedapproach has better accuracy and thus can be used foroptimal design of grid stiffened composite structures.