Along with the breakthrough of networking, communications and information technology, e-commerce gains rapid development in recent years. Trust is the premise and foundation of transaction activities in e-commerce. While conformity is an important factor which influences customers' trust to vendors, as well as customers' choices in online purchasing. Conformity behavior in e-commerce is two-edged. It should be correctly treated and actively guided. In order to understand in depth conformity behavior and its influence, this paper proposes a fuzzy logic approach to model conformity behavior in e-commerce.