In order to solve the duality problem in pose estimation of a single circle in machine vision, an approach based on Euclidean angular constraint is presented to identify the unique pose result.The accuracy of pose estimation is analyzed, which provides constructive suggestions on achieving accurate pose estimation of circles based on experimental results.The pose of single circle is recovered from its projection in an image with a calibrated camera, though the result is ambiguous, only two possible results exist.Then, the unique pose is identified based on the Euclidean angular invariant.Finally, the accuracy of pose estimation is analyzed based on the theory of error propagation.Experimental results indicate that the absolute error of pose angle of the circle plane and the relative error of position determination are within 0.2°and 0.5% m respectively,and the absolute error of reconstructed distance between the two lines is within 0.8%.These results show that the approach can identify correctively poses and positions of circle planes and can offer a high measuring accuracy and reliable results by a simple computing process.