The research of microporous membranes used in Lithium batteries has a major significance all over the world. In this field, the study of microporous membranes obtained from polyolefin by blown film process is highly concerned by many scholars. In this paper, high-density polyethylene (HDPE) was used to study the evolution of the pre-film morphology and its influence on the post-secondary stretching condition through blown film process. Scanning electron microscope (SEM) and Small angle X-ray scattering (SAXS) were used to characterize the orientation of lamellar structure. The molecular chain configuration of HDPE precursor film was characterized by Differential scanning calorimetry (DSC) tests. It was found that through adjusting the blow up ratio and draw up ratio in blown film process, the crystalline structure in precursor film changed from spherulite to lamellae and the lamellar stucture oriented along the machine direction (MD). When the traction speed is too large, the oriented lamellar structure will be destroyed. Key words: Orientation; secondary stretching; high-density polyethylene; microporous membrane College of Polymer Science and Engineering, Sichuan University, Chengdu, 610065, People’s Republic of China. Address: Sichuan University, No.24 South Section 1, Yihuan Road, Chengdu , China, 610065. E-mail: yangmb@scu.edu.cn