Conventional method used in analysis of folded plates structures is based on assumptions stating that the connections between plates in transverse direction are assumed rigidly supported, but actually these connections suffer space displacements and deformations, which emphasizes the no reality of such assumption. Consequently, the actual induced internal forces will be different from those calculated by the conventional method. A comprehensive 3-dimensional analysis using F.E. technique has been carried out for the structure as a whole to clarify the difference of the obtained straining actions compared with the conventional method. The comparison showed that for a certain folded plate configuration and number of vents, there is a great difference in the staring actions in both magnitude and direction depending on the location of the transverse cross section in the longitudinal direction. Furthermore, the forces and stresses in plates in the longitudinal direction showed a significant decrease compared with these obtained from conventional method due to the inclusion of the interaction effect of the different elements of the whole structure. The study covered two important basic common configurations: trapezoidal with vertical plates and triangular with vertical plates. The following parameters are also taken into account: -The number of vents (one vent and four vents). -The angle of inclination between plates. The comprehensive study in this research clarified the great drawbacks in conventional used method, emphasizing the necessity for using the 3-diminsional analyses for the whole structure (Using commercially available computer analysis programs (SAP2000)) to get realistic results.