The numerical simulation shows that the signal of field change detection is sensitive to the optical thickness and effective scale of the cloud in the range of 5° of the forward scattering angle of the sun. We develop a solar photometer (VFOVSP) based on image tracking and automatic fast changing field of view. It can quickly measure the direct radiation of different fields of view and provide a new technical mean for ground measurement of cirrus. The instrument makes use of image tracking technology to solve the problem of four quadrant tracking failure under the condition of thin cloud. A programmable variable field aperture is used to measure the different fields of view in a short time. The aerosol optical thickness (AOT) measured by VFOVSP is compared with that by a solar photometer (POMO2). The root mean square error of the AOT measured by VFOVSP is less than 0.5%, which indicates that the instrument has a high accuracy in the aerosol measurement. The change of the field ratio is analyzed under the different weather conditions. The change of the ratio is related to the particle size and the optical thickness, which provides possibility for retrieving optical properties of cirrus clouds.