In this paper, a boundary-control point (BCP) based motion representation scheme is proposed. According to the scheme, the dense motion field is described by the object boundary and the motion vectors located at predefined grids--the control points. Our scheme differs from the conventional block based motion representation scheme in the point that the motion field has more degree of freedom. It can represent complex motion, e.g., translation, rotation, zooming and deformation. And the motion field is generally continuous, with discontinuity only at the object boundary, so the distortion after motion compensation is mainly geometrical deformation, which is relatively insensitive to human eye compared with the block effect caused by the conventional block based scheme. A pixel threshold criterion is also proposed to evaluate the BCP based motion compensated prediction (MCP) image and to determine whether the MCP error needs to be transmitted. Finally, a BCP based video encoder is constructed. With nearly the same decoded signal-to-noise ratio about 20 - 55% bit rate saving can be achieved compared with MPEG-I, while the subjective quality of the BCP based scheme is better than that of MPEG-I. The new scheme is also quire unlike the model-based scheme for it needs no complex scenery analysis. Some promising experimental results are shown.