To improve the measuring efficiency and avoid the influence from artificial error in the traditional contact method, and to overcome some limits presented in the Hough transform circle detection algorithm that often uses to machine vision, such as heavy calculation amount and inapplicable to the concentric circles detection, a new vision measurement method to measure the ring object diameter is proposed. The proposed method obtains the contour image of object through threshold segmentation and edge detection.Then the Radon transform to the contour image is executed, and the pretreatment result that includes in four light stripes reflects the measuring data of the ring diameter in the all direction angle. Finally, the central lines are extracted from the light strips with the gray gravity algorithm, furthermore the ring diameters are calculated according the distances between central lines. The simulation and experiment indicate that the proposed method holds scientific and reliable measurement result with higher measuring accuracy. Also, it can realize the automatic and non-contact measurement of concentric and eccentric object diameter and hence will hold good engineering application prospect.