In order to introduce a continuous contoured microstructure into the optical thin film, the refraction, diffraction of the microstructures and the interference of the thin film were comprehensively utilized,and the preparation process of the thin film optical microstructure was proposed. The thin film optical tapered grating with anti-reflection characteristics in visible light was designed based on the finite difference time domain method. A tapered grating having a height of 1.6 μm and a period of 4.1 μm was prepared in the SiNx film by single point diamond turning technology, combined with nanoimprint lithography and inductively coupled plasma etching, In the visible band, the SiNx thin film optical tapered grating had an average reflectance of 5.7%, and the experimental results of the reflectance were highly consistent with the simulation results; when the incident angle was within 30°, the anti-reflection characteristic of the thin-film optical tapered grating exhibited an insensitivity to the incident angle of the light waves. It is indicated that the preparation process breaks through the material limitations of the single point diamond turning technology, it can extend the direct formation process of the continuous contour microstructure into the dielectric thin film, and can achieve the anti-reflection of wide spectrum and wide angle.