As the eigen field distribution of the TE0 mode optical waveguide, Rayleigh-Sommerfeld diffraction integral formula and coupling efficiency formula between driving source and receiving optical waveguide are engaged, the expressions of the normalized emission and receiving coefficients of optical waveguide end faces are presented, the expression of coupling efficiency between two non-contact optical waveguides is derived. Then, as the expression of Gaussian approximation for the mode field distribution of optical waveguide is adopted, a compact expression of coupling efficiency between two non-contact optical waveguides is presented. Finally, as the characteristic of the structural parameters of star waveguide coupler is considered, the accumulative operation is replaced by integral operation approximately, the relationship between the total receiving efficiency of receiving waveguides of star waveguide coupler and the basic parameters of this coupler is derived, and the coupling characteristic of this coupler is explained.