Rape straw was chosen as the raw material to produce bio-oil crude (BC) in a vacuum pyrolysis system. BC was vacuum distilled into low boiling fraction (LBF) and high boiling fraction (HBF). Homogeneous aging fraction (HAF) and thick deposited fraction (TDF) were obtained after sealed storage of BC for 90 d. BC was preliminarily analyzed using gas chromatography/mass spectrometry (GC-MS). Chemical structure of samples was investigated using Fourier transform infrared spectrometry (FT-IR). Average molecular weight and distribution of all samples was studied using gel permeation chromatography (GPC). The results showed that BC contained many substances, including water, alkanes, phenols, alcohols, ketones, aldehydes, carboxylic acids, esters, aliphatic and aromatic compound, etc. Frequency shifting and variation of light transmittance from FT-IR analysis showed that the violent movement of electron on different functional groups intensified the interaction of molecular in bio oil. BC and LBF were close to monodisperse system, and HBF, HAF, and TDF were polydisperse system, whose dispersity parameters were 15.85, 7.91 and 20.86 respectively. It was necessary for BC upgrading to improve its stability.