Abstract For detecting exoplanets with high precision, using the angular distance between the two stars to detect the periodic motion of the star will be a better choice. This approach can avoid importing the position error of the reference catalog in the process that uses a traditional photographic plate to derive the star position suffers. At the precision level of microarcseconds, the error caused by optical axis deviation is not negligible. In this paper, we evaluate the impact of the stability of the optical axis on the relative angular distance measurement from the aspects of theoretical analysis and numerical simulation. When the angular distance error limit of 1 microarcsecond is given, the upper limit of optical axis deviation is estimated to be 68 milliarcsecond. In addition, when limiting the deviation of the optical axis, we give the corresponding error allowance of angular distance measurement. Moreover, we also discuss the way to resolve the problem of CCD distortion and focal length change on the measurement of angular distance. The work in this paper is of guiding significance to the design of a telescope.

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