Abstract: Abstract: The effects of annealing temperature, annealing time and tensile stress applying to precursors during the annealing process on the oriented lamellar structures of PP cast precursors and micropore-forming performance by uniaxially stretching were investigated. Crystallinity, lamellar thickness, lamellar crystalline orientation and elastic recovery of PP casting precursors were characterized by DSC, FT-IR, SEM and electronic mechanical tester. Microporous structure was evaluated with porosity and Gurley value. It was found that the oriented lamellar structure of PP casting precursor was gradually improved as the annealing temperature increased from 120℃ to 145℃, leading to an higher elastic recovery value of PP casting precursor and better micropore-forming performance by uniaxially stretching. Further raising annealing temperature, however, would damage the oriented lamellar structure of PP casting precursor, giving rise to lower levels of porosity and permeability after uniaxially stretching. By prolonging annealing time at 145℃, crystallinity, lamellar thickness, lamellar crystalline orientation and elastic recovery of PP casting precursors kept increase at first, and leveled off after 30 min. Applying moderate tensile stress to precursor film during annealing process could increase lamellar crystalline orientation and elastic recovery value of the film, resulting in better micropore-forming performance.