With the view of obtaining symmetric splitting angle prism,on the basis of Bi-,through designing the orientation of the crystal optic axis rationally,make the prism plane-symmetry about center tangent plane;Resulting in splitting beam symmetrically not only for positive-going light,but also reverse direction light. Namely,two-way symmetrically splitting. Futher studies on the relation between rotation angle of the axis and the structure angle of the prism and wavelength,and analyse the symmetry of the splitting angle when apply the prism designed for 633 nm to other wavelength,the results indicate: the asymmetry degree of splitting angle less than 0.24°,in the spectrum range of±300 nm.