In order to meet the industrial requirements of on-line quality evalu ation for semi-transparent thin film,a method of defect inspection and thickness measurement is presented based on machine vision system is presented.The method can retrieve the correspondence between CCD grayscales and thin film thickness,and the CCD grayscales are recorded respectively before and after the placement of thin fil m.By using the same image acquisition hardware and different analysis methods,the system can inspect the s urface defects larger than 0.1mm×0.1mm,and can measure the thickness of thin film in 66mm×50mm area at ea ch time.To reduce the measurement error of thin film thickness based on principle of transmission opti cal density,the density calibration by standard calibration sheet is exploited to correct the density drift of calc ulated density value.PEFT film was adopted to demonstrate the feasibility of the method.The results show that th e average error of thickness measurement is 5.7% with a standard deviation of 6.66%.Assembling with a simpl e scanning module,the two- dimensional surface defects,such as scratch and bubble,can be recognized,and t hree-dimensional full field profile measurement of thin film also can be performed on a general machine vision sys tem.