This paper explicitly highlights the failure analysis and study of thin walled composite beams (multi-cell and multi-tapered) in cantilever configurations when subjected to constrained torsional load, using MSC Patran / Nastran finite element package. Initially, the verification of the model was done with the analytical results in order to ensure the model accuracy. All the multi-tapered beams under examination are composed of closed section and three cell configuration with twisting moment applied at the free end. There is a vivid description of all the effects of different composite material and various stacking sequences on the margin of safety and failure loads. This paper also verifies the influence of various geometrical configurations (Beam lengths, tapered angles and point of variation of tapered angles) of beams on the failure loads. This paper would help in the wing design phase of modern agile and high speed aircraft in which multi-cell closed cross section beams are integral part.