Aiming at the circumstances of time-varying target brightness or multiple targets with different brightnesses,a video amplitude controller feedback system is designed to precisely locate a spot target image on a linear CCD with edge detection by fixed dual thresholds and pixel subdivision by gray weighted centroid algorithm.By adjusting quantitively in tegrating time and program controlling gain,this light adjusting control loop can be kept a constant peak gray value to reduce design difficults for light source and light path and to reduce design cost also.A fixed dual-threshold edge location method is used to truncate a good edge symmetry to aviod the effect of irregularity of the spot peak on location results.Compared with the traditional binarization method with extra external circuits,this system shows its advantages in simple implementation and excellent algorithm,and engineering application gives that it can precisely locate a light spot.Under such circumstance,gray weighted centroid algorithm can reach a better than 1/10 pixel subdivision,so the final spot precise location keeps 2 significant digits after decimal point.Experimental results show that proposed system scheme provides an valuable reference for the future design of multiple-varible light adjusting video system applied in opto-eletctronic measurement.