Optical antenna consisting of objective lens and eyepiece lens plays a very important role in satellite optical communication terminal whether emitter or receiver

and its assembly accuracy were normally assured by interferometer. However

the focus of objective and eyepiece under testing will constantly change corresponding to its design parameter because the operating wavelength of interferometer differs from that of optical antenna. As a result

only the adjustments of lateral optical aberration were accomplished by using interferometer

but the axial spacing between objective and eyepiece was not still determined quantificationally. In order to determine axial spacing of various optical antennas with different wavelengths by utilizing the same interferometer

the relation between wavelength and axial spacing must be studied. In this paper

a relationship between axial spacing derivation of optical antenna and corresponding alterative number of interference fringes was deduced based on optical path difference

hence axial spacing of optical antenna would be adjusted accurately according to this formula. Emulation results proofs validation of formula

and it also shows that corresponding assembly accuracy can meet requirements of satellite optical communication terminal completely.