A new approach capable of analyzing tensile flow curve has been examined by expanding the multiple stra­ta plasticity model. A "flexibility factor", B5, is introduced as a characteristic parameter to express active slip systems in a polycrystalline metal. It is defined by the ratio of grains having more than five activated slip systems to the total mumber of grains. The active slip systems can be computationlly evaluated for a virtual polycrystalline specimen. A plastic potential function and an intermal structure variable, which are the fundamental descriptive functions in this model, have been evaluated by comparing the plastic con­stitutive equation with the tensile flow curve of a pure copper. It has been clarified from the analyzed results that the variational feature of an internal structure variable A is closely related to the changing beha­vior of B5, in whole strain region.