Abstract: The relative position and stability between primary mirror and aspherical secondary mirror(SM for short) is important to test and checkout for the collimator. First, the supporting system of secondary mirror was analyzed according to the theory, and the dynamics model of supporting trusses was built. Then, the secondary supporting system was designed, optimized according to the disposal of decreasing dimension by FEA. Finally, effects caused by temperature were analyzed. The results show that tangential spider van support could reduce the masking and keep the stiffness at the same time. The ratio of rigidity of the improved supporting truss is uprated, which make the 1st resonance of the whole system arrive at 62 Hz. The effect of temperature also can be decreased by change material of local structures, making the wavefront error of system change from /20 to /30. The scheme has fine accuracy, well stability and meet the design requirement.