In dual-frequency laser interference measuring system Wollaston prism is anindispensable and important device,which can separate the incident beam in to measurement beam andreference beam according to the polarization direction of dual-frequency laser,so as to realize the highaccuracy measurement. But if the installation orentation of Wollaston prism relative to the incident beamand the distance between the prism and the focus lens are different. The measurement result will bedifferent. In this paper,combining with the surface roughness laser measuring system,the influence ofthe orientation of Wollaston prism on accuracy of measurement is analyzed in theory and quantitatively.