采用有限元方法分析了单棱镜在重力作用下三个典型位置的表面变形，对棱镜表面Φ425 mm通光孔径轴向变形量进行Zernike多项式拟合，画出了相应的波差图，并确定设计方案．进一步选择Φ360mm口径光束对双棱镜在几种典型相对位置下进行光线采样、追迹，计算得到不同情况下由于双棱镜自重变形引起的总波差．

Firstly finite element method is adopted to analyse surface deformation of a single prism under gravity when it is in three typical positions,and Zernike polynomials are fitted for Φ425 mm axial deformations of the prism surfaces,corresponding wavefront error figures are plotted,a design of prism is choosed. Then Φ360 mm light beam is sampled and ray tracing for double prisms in several typical relative position,and corresponding total wavefront error of double prisms under gravity are computed.