High precision automatic tracking system is indispensable component of solar concentrator. Whether signal collector gathers the signal from sunlight direction accurately and reliably or not is the key of automatic tracking accuracy. A design scheme about signal acquisition device of rough and fine adjustment complementary was put forward. One set differential-mode signal could be automatically chosen from two sets sensors by the software during normal work. The scheme effectively resolved the contradiction between a large range looking for the sun and high accuracy tracking. A new structure of collection the signal of concentrating solar was improved, which could solve the problem of photoelectric sensor go into saturated zone in the large light intensity and the output differential-mode signal is too small when the light intensity is very weak. According to the principle, a made signal acquisition device of concentrating solar with rough and fine adjustment complementary was applied to the company′s CPV type 1200W GaAs power generation systems, and achieved very good tracking result with the actual tracking error ≤0.1° (solid angle).