Abstract: Optical parallelism errors caused by the angle errors of pentagonal prism,which is generated in manufacture process, are analyzed, and the formulae for determining incidence ray and adjusting prism are derived. The dependence of the output plane wavefront of pentagonal prism on the angle errors of pentagonal prism and kinematical errors caused by guide rail is established according to the prism rotation theorem. The wavefront error of scanning beam turning caused by the angle errors of pentagonal prism and the kinematical errors of guide rail was analyzed with computer simulation. This study is useful to pentagonal prism manufacture process and adjustment, and helpful to correct wavefront error of scanning beam turning during wavefront measurement of large aperture telescope.