Abstract: A novel 3D model analysis of circular feature is addressed in this paper for machine vision. We use an efficient method for fitting ellipses to data points by minimizing the algebraic distance subject to a constraint, which a conic should be an ellipse, and solve the ellipse parameters with Lagrange multiplier method. After analyzing the perspective model of circular feature, the 3D position and orientation of a circular feature with known radius is obtained using closed form solution. A set of identical circles are detected with the model analysis. Experimental results show that our method is efficient and accurate.