The influence of structure parameters on mechanical properties of honeycomb sandwich mirror was investigated. Gibson hexagon equivalent theory, sandwich plate theory and Hoff theory were modified based on the theoretical analysis. The results were shown that structure parameters had non-linear influence on dimensionless structure tensile specific stiffness, shearing specific stiffness and bending stiffness in different direction while the honeycomb core was equivalent as solid material with modified material properties. The honeycomb mirror and equivalent model was modeled by using finite element method. The root mean square (RMS) and peak-to-valley (PV) values of mirror surface were determined under gravity with the optical axis pointed to the zenith. Compared with the actual modeling data, the relative error of equivalent results was less than 5%. And the optimal structure parameter range was obtained by these analyses.