Rapeseed were pretreated by steam explosion at 0.4, 0.7 and 1.0 MPa and at maintenance pressure for 1 and 3 min. The low temperature pressing method was used to separate rapeseed cake and oil, and their polyphenol yield, composition and antioxidant capacity were determined respectively to investigate the effects of steam explosion pretreatment on them. The results showed that the color of the prepared rapeseed oil was gradually deepened by either increasing the bursting pressure at the same dimensional pressure time or increasing the dimensional pressure time at the same pressure. After the steam explosion treatment, the polyphenol yields of rapeseed cake were 7.12-8.42 g/(100 g). The polyphenol yields of rapeseed oil were significantly increased with the highest polyphenol yield 0.56 g/(100 g) at the time of dimensional pressure for 3 min at 1.0 Mpa. 2,6-dimethoxy-4-vinylphenol(canolol), catechins, caffeic acid etc were generated in rapeseed cake, of which canolol had the largest amount of conversion generation and part of it migrated to rapeseed oil, and the contents of canolol in rapeseed cake and oil reached the maximum when the dimensional pressure was maintained for 3 min at 0.7 MPa, which was 12 120.00 and 4680.00 mg/kg. The antioxidant capacity of rapeseed oil extracts determined by DPPH, ABTS and FRAP methods was significantly increased, while the antioxidant capacity of rapeseed cake showed a smaller change. A significant or highly significant positive correlation between polyphenol yield and antioxidant capacity of the extracts were observed. It can be seen that steam explosion can be used as an effective technology for pretreatment to improve the polyphenol content and antioxidant capacity in rapeseed oil, and steam pressure of 0.7 MPa, dimensional pressure of 3 min can be used as an optimal steam explosion conditions for the processing of rapeseed.