Abstract: According to the working characteristics of equatorial telescope, the supports scheme on 700 mm primary mirror were designed. The finite element model of the system was established by the software MSC. Patran. The surface deformation under gravity was analyzed in different load cases. The curves of surface deformation errors PV and RMS were plotted. As a result, the surface deformation is influenced mostly by angle , and it decreases when the angle rises. The effect of the radial support is better than the axial support. The surface deformation errors can satisfy the precision requirements. When the system is perpendicular, the test result of RMS is 28.48 nm by Zygo interferometer, which shows that the surface shape with the supports is close to the test state. It validates that the finite element model is accurate.