In decision-making tasks, groups are often expected to achieve better decision quality than individuals because groups possess various information from their members. But a lot of research results showed that groups are not as effective as expected in using the various information. Groups tend to focus more on the information possessed by all members (shared information) than on the information possessed by an individual member (unshared information). This phenomenon is called “Shared Information Bias “(Stasser & Titus, 1985). The existence of shared information bias hinders the groups from achieving better decision quality. Based on the hidden profile paradigm, this paper illustrated the mechanisms of shared information bias from four perspectives, namely information sampling model, dynamic collective information sampling model, mutual enhancement effect, and preference effect. Also, this paper summarized the roles of four influential factors including information distribution, group task characteristics, member characteristic, and motivation factors. Future researches could focus on combining the team cognition, exploring the influences of affective factors, and integrating the group decision effectiveness model.