Abstract: Determining the 3-D relative motion between the camera and the viewed object is an important topic in the field of computer vision. Assume that there are some feature points on the object and their positions in space have been recovered by the stereo vision, this paper discusses how to estimate the motion parameters from the observed position vectors of the feature points. The objective function available in the literatures lead to a nonlinear optimization problem. A new objective function based on the Cayley's heorem is presented in this paper. The relationship between the two objective functions is also discussed.