Abstract: Owing to the unique physical structure and excellent photoelectronic properties, two-dimensional (2D) materials have attracted more and more interest from researchers, which shows a huge potential for the applications of photodetection area. The 2D material-based photodetectors currently studied mainly belong to photon detectors. Their photodetecting porcess involves the directly photoelectronic conversion. The key point to the accomplishment of the 2D material photodetectors of high performance is to fully utilize photo-to-electric conversion mechanisms and take their advantages in the aspects of device performances and functions. By tracking previous works of the authors' research, the directly photoelectronic conversion mechanisms of photodetectors was investigated and the recent progress of 2D material-based photodetectors in terms of their performance enhancement, development of photoelectronic conversion mechanisms and structure design of devices was summarized. Finally, an outlook on the challenges and opportunities for 2D material photodetectors was presented.