In the first section of the "curved motion" of high school physics, the synthesis and decomposition demonstration experiment of motion has problems such as unintuitive experimental phenomena. A motion synthesis demonstrator is newly designed and made, the demonstrator is mainly driven by the motor screw nut transmission device to work, the instrument uses the screw nut drive mechanism in the horizontal and vertical directions to drive the soft pen to move, and the motion synthesis trajectory can be drawn on the white organic board through the soft pen. The experimental phenomenon of the device is intuitive, the structure is simple and clear, the production is convenient, and the demonstration operation is easy to promote.