In order to improve the availability of solar energy and solve the problems of time-varying and dispersion of sunlight, a kind of automatic tracking system for sunlight signal acquisition is introduced based on photosensitive resistance. A new type of eight points hemisphere sun azimuth signal sensor is designed. Through position distribution and combination of the two groups of sensors in the tracking system, coarse and fine tuning together, the sun azimuth signal is searched in a large range and adjusted in a small range so as to control the tracking system to realize tracking the sunlight accurately and automatically. The internal structure design and the principle of the sunlight azimuth signal sensor, the control process and the principle of the automatic tracking system are analyzed. Experimental results show that a high precision automatic tracking is realized in the case of low cost, a strong anti-interference and practicability, which has a very vital significance for the solar energy application promotion in the field of photovoltaic and thermal power generation.