An approximate result of first neighborhood is given in ref [5] . In consideration of the importance of strict treatment about this problem, a new formula is derived. According to the computational comparision between the two formulas, it can be concluded that the approximate method in ref [5] is very simple, convenitnt and reliable. It is also concluded by adding random errors to the magnitudes of normalized structure factors that Hauptman's conclusion, namely, the two-phase structure invariants are only dependent on chemical composition and independent of the structure factors, is still correct in the two-wavelength case. Considering this fact, we suggest a fast computational method of the two-wavelength struc-ture invariants which may be useful in practical macrostructure crystallography.