The classic deformation mechanism of the Gaussian model of Haward and Thackray was utilized to treat the true stress strain behaviors of a family of novel polyether-bamide segmented copolymers based on the crystalline hard segments of polyamide1012 and the amorphous soft segments of poly(tetramethylene oxide). The results showed that the deformation behaviors of the plastic copolymers abided by the Gaussian model, causing the modulus G of the strain-induced hardening process to depend on the weight percentage of the polyamide segments in the copolymers. By contrast, the deformation of elastomeric copolymers deviated from the model because of the occurrence of strain-induced crystallization in the soft polyether sections at large strains, which negated the Gaussian assumption; i.e., the random coil conformation was maintained even under substantial stretching. The onset point of deviation was, for the first time, quantitatively identified by in situ FTIR and further confirmed by in situ WAXD/SAXS.