Based on the double refraction principle of outgoing beam in the biprism,the displacement method for measuring the small angle of biprism is presented.The error of this method is also discussed.

• 利用双棱镜引起出射光束方向双向偏折的原理；提出了一种位移法测量玻璃双棱镜微小底角的新方法；介绍了测量的基本原理；讨论了测量误差.