Abstract: Based on the global sensitivity analysis for structures with uncertainties, the effects of uncertainties of input variables on the variance of output response of composite structures and failure probability were investigated. Considering the uncertainties of mechanial properties of material, ply orientation angles, ply thickness and applied loads, the uncertain propagations of inputs on output responses displacement and strength ratio were analyzed using the global sensitivity analysis supported by the variance-based method and the method based on failure probability. The numerical example of the composite I-beam validates the effectiveness of sorting results, which are useful for the stable optimization design of composite structures in engineering.