Cross-sectional analysis of a composite box-beam is performed by an analytical method and a variational-asymptotical method. The beam stiffness coefficients are obtained and compared for both analytical and variational-asymptotical methods. The parameters of box­ beam width and height, wall thicknesses, initial twist and composite orientation angle are selected for the sensitivity of box -beam stiffnesses. The sensitivity results give the most important parameters affecting the stiffnesses of the box-beam.