Abstract: The circular structured light sensor is composed of a laser projector, a cone-shaped mirror and a camera. The laser is reflected by mirror and intersects the objects surface, the camera captures the relevant image. Based on the analysis of the imaging geometry, a fast calibration method employing multiple rings is proposed to determine the key parameters of the light surface. The measurement error is ±0.2mm for the diameter measuring by the calibrated sensor. The proposed calibration method is easy to realize, able to meet the on-line requirement with the certain accuracy.