Alluvial fan is an important depositional system developed on the edge of the basin. Compared with other depositional systems, the research degree of alluvial fan is relatively low. However, more and more attention has been paid to the study of alluvial fan in recent years. Internationally, alluvial fan study is still in the exploration and development stage due to the extremely complicated depositional mechanism and evolution process. And the classification of alluvial fans is still internationally controversial. Accordingly, this paper is focused on the genetic mechanism of alluvial fans and makes a systemic summary of the sedimentary geomorphic element, sedimentation types, depositional mechanism, depositional model and controlling factors on basis of a large number of research literature. Furthermore, a new genetic classification scheme of alluvial fan is proposed. Research results show that alluvial fan can be classified into 4 types, namely bedrock related，episodic, fluvial and special fans. Additionally, episodic alluvial fans can be further classified into 5 subtypes, namely debris- flow fans, sheetflood fans, unconfined streamflood fans, episodic fluvial fans and transitional fans. In contrast, fluvial fans can be further classified into 3 subtypes, namely single river dominated fans, multiple river dominated fans and terminal fans. However, along with the deepening of research, this classification scheme will be constantly improved. Overall, this paper is intended to introduce the international research progress in depositional mechanism of alluvial fan and make a discussion on genetic classification, which can provide a valuable reference for the development of sedimentology on alluvial fan.