Two-dimensional structures like plates and cylindrical shells must be analyzed in the two directions simultaneously to get a true analysis of these structures, but in traditional methods these structures are analyzed by solving each direction alone as one-dimensional structures without taking into consideration the effect of the other direction. This approximation in analysis tends to give big differences in deformations, displacements, and straining actions. Due to theory of plasticity, the plane strain in X-direction tends to contribute of strain in Y-direction. To make a fruitful comparison between spatial and traditional methods one model solved in textbooks was taken into consideration. This model is a cylindrical shell solved by spatial method with the same conditions of the solved traditional method model, but with 3-d model. The straining actions of two methods were compared. Normal force in the spatial method was bigger than traditional method by 4 times, the transverse bending moments in traditional method were much bigger than corresponding values in spatial method by values ranging between 40- 140%, and the longitudinal normal stresses in traditional method were bigger than spatial method in compression by 40% and in tension by 100%. This proved that traditional method overestimates the straining action and stresses compared to the spatial method based on 3 dimensional analyses.