The sunbeam can be converted into electricity via photovoltaic solar cells, and sun trackers are such devices for efficiency improvement. In this paper, different types of sun-tracking systems are reviewed, such as fixed tilt-angle, dual-axis, single-axis with East-West direction, and single-axis with North-South direction. The captured irradiation using different sun trackers are compared, and different influence factors are analyzed to gain the optimal orientation of the sun, such as time error, latitude, azimuth angle and tilt-angle of a photovoltaic module, reflectivity, and composite transparent coefficient. These results are very important to improve the tracking efficiency of the sun tracker.