Abstract: In this paper, we present a method of the recovery of the 2D rigid motion and structure from a 1D orthographically projected optical flow field. The geometric model and mathematic model of a moving rigid object are set up. It is proved that the 2D rotation parameters can be determined at least by using three optical flow points. In general, there are two groups of rotation parameters. Although the translation parameters are not obtained completely, the 2-D structure of the rigid object can be determined uniquely. A computing example is given.