The observation system of solar velocity field can be used to detect the activities of helioseismology, which is important for the study of the solar internal structure. The method of using K-FADOF to observe the velocity field of photosphere is studied, which takes advantage of the Faraday anomalous dispersion optical filter (FADOF), such as high spectral resolution and spectral stability. This method utilizes K-FADOF to distinguish the Doppler shift of potassium line (769.898 nm) which comes from the Sun′s Photosphere, uses the F-P etalon to select the single-peak signal transmitted through the K-FADOF, and receives photosphere′s Dopplergram. The prototype of K-FADOF is developed and tested. The experiments show that its experimental transmission spectrum pattern almost coincides with its theoretical pattern. It indicates that the K-FADOF meets the requirements of observing the solar velocity field of high spectral resolution. Further, it can achieve to observe simultaneously multi-layer velocity field of the solar atmosphere with this technology extended to the solar other lines.