An advantage of stereovision-based motion analysis is that the depth information is available, thus motion can be estimated more precisely in 2.5 D stereo coordinate system (SCS) constructed by the depth and the image coordinates. In this paper, stereo global motion in SCS, which is induced by 3D camera motion in real-world coordinate system (WCS), is parameterized by a five-parameter global motion model (GMM). Based on such model, global motion can be estimated and identified directly in SCS without knowing the physical parameters about camera motion and camera setup in WCS. The reconstructed global motion field accords with the spatial structure of the scene much better. Experiments on both synthetic data and real-world images illustrate its promising performance.