Abstract: Single crystal germanium material diffractive optical element (DOE), which possesses unique negative chromatic dispersion and thermal expansion coefficient, has been widely used in the IR optical field. DOE requires optical surface and transition of phase profile well. Micro-circle single point diamond turning is one of the ways to solve it. Actually it's difficult to have the proper cutting tool parameters to fit the surface roughness and the transition of phase profile. So there is great sense to study the micro-circle single point diamond turning of DOE. This paper studied the roughness of single crystal Germanium materials affections on the turning parameters and the tool parameters by using the DEFORM 3D software. Then the test was done according to the optimization results of the simulation. The results show that the surface roughness is 4 nm when the micro-circle radius of single point diamond turning is 0.1 mm.