Abstract: The normalized structure factor module and phase withanomalous scattering(|E_H|,|E_H^-,φ_H、φ_H^-) are calculated with the crystallographic data of a medical small molecule crystal C₁₈H₂₄NO₄Br. Then the two-possible ambiguity of the phase,Φ_H or Φ_H^-,is obtained by Harker construction, if the|E_H|,E_H^-| and the coordinates of the anomalous scatterer Br are known. The probabilistic estimate of two-phase structure invariants, W=Φ_H + Φ_H^-=-ξ, is used to identify the correct solution of the phase in two-possible ambiguity. The computational results show that the probabilistic estimate Hauptman's formula for C₁₈H₂₄NO₄Br is as useful as that for another crystal C₁₈H₂₄NO₄ I.