The cross-linked phase in real cross-linked rubber behaves as not the non-Gaussian but the Gaussian. The stressupturn and high tensile strength can be realized by the contribution of the co-continuous uncross-linked phase. The uncross-linked phase changes to the bundle of the extended molecules under large extension at a low temperature and high velocity depending on the molecular packing, which supports the main part of the stress of the system. For NR, due to its high molecular stereo-regularity, the molecular packing in the uncross-linked phase increases greatly as extension increases, and thus the stress-upturn and high tensile strength will be well generated even at room temperature.