Structural evolution of two ethylene-octene copolymers with different octene content during tensile deformation and recovery was investigated using the in-situ synchrotron small-angle X-ray scattering technique. Sample containing 4 mol % octene shows similar deformation mechanism as observed previously that the whole process of deformation can be regarded as a stretching of two interpenetrating networks of crystalline rigid network and entangled amorphous phase. A transition from a crystalline rigid network dominating behavior at small deformations to a stretching-induced crystalline block disaggregation-recrystallization process occurs at a critical strain where stress generated by the stretched amorphous network reaches a critical value leading to the destruction of crystalline blocks. In sample containing 8 mol % octene, this critical strain is much larger than observed in the other sample. Such a phenomenon is attributed to the fact that only crystalline lamellar stacks and bundle-like crystals with much weakened coupling can be developed in the sample. The weakened coupling between crystalline lamellar stacks is due to the existence of interstack amorphous phase which also leads to an inhomogeneous strain distribution in the system.