By considering the poor monitoring conditions of universal coating equipments with low stability,precision and automation level,a new kind of photoelectricity-control-analysis system was developed.Based on double-frequency modulation,a photoelectric test system with four-light beams was put forward.A dual-lock-phase circuit system and a comprehensive digital processing system with compound filter were used to process monitoring signals,and all automation-monitoring functions were achieved with a control-analysis system.The experimental results show that standard deviation of Thin Film Thickness(TFT) is equal to or less than 0.55%,and signal-noise ratio approaches to 1 000.A very good linearity of numeral display is obtained and the display resolution limit on reflectivity is 0.02%.The linearity of static drift is very high,the drift ratio is less than 1.95%/h,and the static stabilities are double superior to that of universal system.It is concluded that proposed system has advantages of the static and dynamic stabilities,the signal-noise ratio,and the control precision for TFT.