Isotactic polypropylene (iPP) precursor film with highly oriented lamellar structure was produced through a melt extrusion-annealing-uniaxial stretching (MAUS) process. The precursor films were annealed at various temperatures and the structure evolution of precursor films during various annealing temperatures and the pore formation of the annealed film during stretching were investigated. During annealing, recrystallized lamellar structure was formed to obtain “core-shell sandwich” structure. The thickness of newly formed lamellae increased with annealing temperature, which improved the ability of slipping resistance of the original lamellar structure during stretching. As the annealing temperature of precursor film increased, the micropore shape and diameter of the final membranes became more uniform. The porosity of the microporous membranes increased with increasing annealing temperature.