Aiming to unveil the effect of cold stretching conditions including strain and temperature on the morphology and performance of membrane product, high density polyethylene (HDPE) microporous membranes were prepared by uniaxial stretching. The evolutions of lamellar stacks and micropore formation were tracked by combining in-situ and ex-situ X-ray scattering and scanning electron microscopy methods. It was found that cold stretching strain mainly affected separation degree of lamellar stacks under strain lower than 60%, while slip of crystal at higher strain. As for cold stretching temperature, stretching below 60 degrees C can promote separation of lamellar stacks, while stretching over 80 degrees C is beneficial to pull out molecular chains from lamellae, resulting in fibrils. A linear relation between separation degree of lamellar stack and air permeability of final membrane was established, which can provide guidance for producing HDPE microporous membranes with high performance. (C) 2016 Elsevier Ltd. All rights reserved.