Continuous bundles of aligned electrospun polyacrylonitrile (PAN) precursor nanofibers of different stages in electrospinning process were prepared with a flowing water bath collector. Then the as-electrospun nanofiber bundles were stretched in hot water at 97 degrees C into 2 and 3 times of the original lengths. Subsequently, characterizations and evaluations were carried out to understand their morphology, diameter, density, crystalline structure and orientation using SEM, WAXD etc. The study revealed that; (1) the polymer solution jet was stretched/elongated during electrospinning process, which formed and improved the crystalline structure and orientation; during the electrospinning process, the diameter of as-electrospun nanofiber bundles was decreased from 664 nm to 353 nm, while the crystallinity and the orientation increased from 42.55% to 47.76% and 37.48% to 43.93%, respectively, which led to the density increased from 1.1917 g/cm(3) to 1.1943 g/cm(3); and (2) the improvement of the crystalline structure and orientation was limited when most solvent was removed during the electrospinning process, and post-spinning stretching could substantially improve the crystalline structure and orientation. Meanwhile,the improvement of the crystalline structure and orientation of as-electrospun nanofiber bundles could enhance the post-spinning stretching process.