The fast fashion industry is criticized for its unsustainable development. With the rise of the green economy and the awakening of consumers’ awareness of sustainable consumption, more and more companies realize the significance of green marketing in improving brand performance. However, it is undeniable that many fast fashion companies tend to take advantage of information asymmetry and cover up the unsustainable part of their business activities through fake green marketing campaigns to gain more potential consumers. There is a limited number of green marketing studies investigating consumers’ perception of greenwashing, while it is naturally important to explore the demand side responses to greenwashing in different industries. Therefore, this paper examines whether and how consumers’ perception of greenwashing in the fast fashion industry impacts their green purchase intention. The study explores the mediating role of perceived risk and the moderating role of consumers’ impulsive buying. In this paper, 433 valid questionnaires are collected from mainland China, and the Partial Least Square-Structural Equation (PLS-SEM) is used to test the hypotheses. We draw the following conclusions: (1) consumers’ perception of greenwashing in the fast fashion industry has a direct negative effect on their green purchase intention; (2) greenwashing perception has an indirect negative effect through consumers’ risk perception, including financial perceived risk and green perceived risk; (3) consumers’ impulsive buying in the fast fashion industry reinforces the positive effect of greenwashing on their financial risk perceptions as a moderating variable. The conclusion of this paper has implications for the sustainable development of China and other emerging economies, which highlights the importance of pursuing information symmetry in green marketing to reduce consumers’ perceived risk and encourages companies to make substantial, sustainable development initiatives.