The study of supermassive black hole (SMBH) is one of the most confusing astronomical topics. Howerver, little is known about the co-evolution of SMBH and galaxies, and also the formation process of SMBH. SMBH is considered to be a celestial body on the cosmic scale. As a probe, SMBH plays an irreplaceable key role in the study of the structure and evolution of the universe. The above-mentioned scientific researches requires 10 micro arcsecond astrometry precision. Based on the differential delay interferometry, we plan to develop a prototype long baseline optical interferometry facility to achieve high precicsion astrometry. The planned prototype facility includes three 500mm siderostats, and the detection waveband covers both near infrared and short wave infrared (J, H). The astrometry precision of the prototype facility is expected to be at the level of ten micro arcseconds.