For the measurement of complicated deep hole profile

both eddy current method and ultrasonic method characterize low accuracy

at the same time

optical scanning with single light point has low efficiency. A 3D measurement system based on ring-structured-light is presented which characterizes high accuracy and processing speed. A data processing method using FFT analysis and difference analysis has been proposed. The system consists of a ring-structured-light generator

a reflection cone mirror

an imaging cone mirror

an optical lens

and a CCD camera. Firstly

we capture a structured-light image of the measured inner surface and extract the stripe center locus of it. Then we find the center of the stripe center locus by curve fitting using the least squares method. Subsequently

we stretch the stripe center image from its center point. In the waveform of the stretch-out-view

there exist eccentricity error and ellipse shape error. The frequencies of these two periodical error components are different from the frequency constitution of the detail component. We can separate them from the waveform with the help of FFT analysis. Therefore the eccentricity error and the ellipse error can be minimized and the accuracy of the system is improved greatly. Difference analysis was used to remove the transition line between the exterior circle and the inner circle. The method can improve both the accuracy and the efficiency of the inner surface parameters measuring. Experiments show that the diameter measuring accuracy can get 0.05mm.