The invention discloses a sun photometer measuring cirrus cloud optical characteristics; a host industrial control computer sends a measuring order, determines the initial position, and starts a sun visual locus tracking order; a program calculates horizontal and pitching motor steps needed to turn to the sun orientation, and sends the data to a lower computer embedded control system; the lower computer embedded control system controls a motor-driven system to rotate the horizontal and pitching motors, thus enabling a probe to turn to the current sun orientation; when the sun image appears ina CCD probe visual field, CCD image fine tracking is started; the sun lights pass the tracking imaging optical system, and irradiate on the target surface center of the CCD probe; the sun images in the visual field are gathered and stored, and sent to the host industrial control computer; the host industrial control computer analyzes the gathered images, thus determining whether the sun is finelytracked or not. The sun photometer employs the image tracking technology to replace the four-quadrant tracking, thus realizing all-weather tracking, and realizing large field of view tracking.