Facial stimuli are quite different from usual objects, and the purpose of perceiving human facial stimuli is also very different from that of perceiving usual objects. We perceive objects is just to understand what and where they are, but when we perceive a human face, in addition to identifying a face, we also want to know how it differs from other faces. Sometimes we want to infer the information about age, sexuality, or race from the face. More importantly, we need to understand the facial expressions, especially the emotions that faces express, so that we can react appropriately when we communicate with others face to face. Considering these purposes of face perception, we propose that face perception includes the following four aspects: face detection, physical attributes detection, biological attributes detection, and social attributes detection. This may help scientists to clarify the roles of related brain areas including FFA in face perception more clearly. Although FFA is a core brain area for face processing, its exact roles remain unclear. We reviewed related studies and analyzed FFA’s roles in the four aspects of face perception. Firstly, we focus on that whether FFA is essential to confirm a stimulus is a face. Although FFA shows its activation both for usual objects and faces, stronger activation for faces than for usual objects has been confirmed by many studies. It suggests that compare to usual object detection, FFA is more sensitive to face detection. Therefore, we conclude that FFA is essential to confirm a stimulus is a face. Secondly, we discuss whether FFA plays a crucial role in distinguishing a face from other faces based on their physical attributes. Although some studies emphasize that FFA’s activation has a holistic domination, and others insist that FFA is sensitive to local features, what our concern is if FFA’s activation is dependent on difference of faces. Actually, if a face is perceived as a different face, FFA’s activation also changes. Based on the fact, we summarize that FFA plays crucial role in distinguishing a face from other faces based on their physical attributes. Thirdly, we consider the role of FFA in biological attributes detection. Some studies indicate that FFA’s activation is dependent on sexuality, age, and race of a face. Thus, FFA also plays role in biological attributes detection. Finally, we focus on FFA’s role in social attribute detection. Currently, there have been contradictory results about the relationship between FFA’s activation and some social attributes like expressions of a face. Some studies indicate that different FFA’s activation reflects different social attributes while other studies show there is no correlation between FFA activation and social attributes of a facial stimulus. Since social attributes of a facial stimulus are very complex, it is not easy to get coherent results. Face cognition is a purposeful cognitive activity. Classifying the purposes, and then clarifying what roles the related brain areas play in achieving the purposes, is an effective approach to understand the mechanisms. Besides FFA, there are also other face processing brain areas such as OFA (Occipital Face Area) and STS (Superior Temporal Sulcus), and same approach can be adopted to clarify the roles of these areas. More knowledge about the functional roles of all related brain areas in four aspects of face processing we get, clearer the neural mechanisms of face processing will be.