Two methods and their experiments for laser beam autocollimation areintroduced, the phase step method is based on spatially modulating the incident laser beamby a phase step plate3 and the phase dot method, by passing through the phase dot, thediffraction phenomena of both incident beam and reflected beam are utilized. Theintensity distribution modulated by both phase shifting plate are analyzed based onFraunhofer scalar diffraction theory. The experimental results are presented as well.