view of the problems existed in the traditional directional interference system,such as complicated structure,oversize dimension,difficult to zoom and color difference,a laser beam expanding system with the reflective off-axis opto-mechanical structure was designed.The optical-mechanical structure of off-axis double reflectors were designed and analyzed.Analysis results show that the maximum deformation is below 0.01 mm,the frequency of basic vibration was 105.2 Hz,and the maximum stress of the structure is less than yield strength of the material.After testing,the beam expanding ratio obtained is 1∶15.01(19.96,25.03) and the spatial offset errors is below 1mrad,which meets the requirement of technical index.