Four different molecular weight iPP samples were first quenched into the ice water, and then stretched at 140 oC to a certain strain to obtain highly oriented structure via die- drawing approach. After above-mentioned procedures, the overstretched samples were cut to 0, 45 and 90o directions along the pre-orientation used for further deformation experiments at high temperatures. In such case, the critical stress of whitening at large strain was found to be depended on both of molecular weight of iPP and the pre-oriented direction. Generally, for the same direction, the value of critical stress of whitening was increased with increasing iPP molecular weight, and which was agreement with our previous report. Meanwhile, for one molecular weight iPP, the critical stress of whitening presented a smallest value in 0o sample but a largest value in 45o one. This behavior may be caused by the process of second orientation of molecular chains and disentanglement of the new developed highly oriented amorphous network initiated by the breaking of inter-fibrillar tie chains. Acknowledgements: This work is supported by the National Natural Science Foundation of China (21134006) and Royal Society-Newton Advanced Fellowship (NA150222).