Abstract: A mathematic model for dual-wedge prism system is proposed to analyze the refractive property of light. By use of the theories of geometric optics and scalar diffraction, it is found that the dual-wedge prism can be simplified as a single-wedge prism whose angle between two refractive planes and main optical plane are changed with the rotary angle between two wedges. When these two wedges rotate in the different angle speed and opposite direction, the refractive light from this system is in two dimensions. Besides, taking the dual-wedge system as a diffractive screen, a theoretical analysis is made on the diffraction light field distribution of the beam which passes through the rotary dual-wedge system. Under the condition of Fraunhofer diffraction, the variation law of diffraction light spots with the rotary angle was obtained. This research may give a developing direction for the 2-D controllable scan.