Some products are subconsciously thought to be seldom purchased online, but in fact search online this paper have found a large number of online purchases, such as bra. So what are the characteristics of this kind of product? From the perspective of outlier knowledge, this study analyses why consumers buy such products, who is buying, what’s the relationship between grey product and purchasing behavior. The research process of this paper is as follows: Firstly, the consumers who buy bra online are interviewed by field interviews, and the different effects of the attributes of such products on consumers are summarized from the perspective of outlier knowledge. Secondly, the influencing factors privacy concerns and purchasing behavior in the model are measured by the previous maturity scale, while the grey products knowledge is revised by using Bruck's scale for reference. Finally, sample data are obtained by questionnaire. This study finds that privacy concerns have a negative impact on consumers' online purchasing behavior of grey privacy products and consumers' grey products knowledge has a significant positive impact on consumers' purchasing behavior from the perspective of outlier knowledge. Discussing the factors of consumers' online purchasing behavior from the perspective of outlier knowledge management can provide a new perspective for follow-up study.