According to the long focal length wide-field off-axial three mirror system of high quality in space telescope

the majorized issue of the opto-Structural System was discussed. To design the lightweight precision truss

which is fitted to characteristic of the light high resolution space camera

the method of mode analysis and the principles of designing the main truss are studied. Then the analysis of its supporting structure was made by means of FEM(Finite Element Method)and optical design software. It has proved that the performance such as self-weight deflection

fundamental frequency

thermal stability of the long focal length wide-field off-axial optical system all meets the requirement.