Based on Helmholtz-Kirchhoff diffraction integral theorem, the relationship among micro-structure parameters, incident light parameters and transmission light parameters of achromatic uniform light thin film are theoretically derived. The influences of micro-structure parameters on transmission light amplitude distribution and scattering angle are analyzed. When light beam passes through the achromatic uniform light thin film, the scattering light spot has many advantages such as uniform light intensity distribution, achromatism, controllable scattering angles and wave shape. The thin film with the maximum depth of 5 μm and scattering angle of 8°×7.5° is fabricated. The error of measured scattering angle and the theoretical angle is within ±0.5°. The designed thin films can be used in illumination, LCD backlight display, projection system as well as other applications.