Previous studies of advertisements revealed the potentially misleading or deceptive effect of vague language used in advertisements, but failed to explore the socio-psychological mechanism behind the use of misleading or deceptive vague discourse. In view of this research gap, the present study, adopting the methods of audience survey and interview, aims to investigate the socio-psychological factors adapted to by advertisers in the use of misleading vague discourse within the framework of critical pragmatics. The analysis shows that TV shopping advertisers tend to focus on prospective customers’ psychological tendencies (such as blind belief in high technology and authority, pursuit of cheapness and novelty, crowd mentality, etc.) and adapt negatively to those mentalities in the use of vague discourses so as to mislead the customers into buying their products. This study could provide some reference for the government departments concerned in their supervision and management of the TV advertising programs.