The conditions of color-reaction of boric acid with 1-(2-hydroxy-3-methoxybenzylidence-amino)-8-hydroxynaphalene-3-6-disulfonic acid in buffer medium of ethamine at pH 6.5 were studied in the assy.The maximum absorption wavelength of this coordination compound was 420 nm.The coordination reaction showed a good linear relationship at the concentrations of boric acid of 0.4～0.6 mg/L.The detection limit and molar absorptivity (ε) was 0.08 mg/L and 4.6×104 L/(mol·cm) respectively.This method presented perfect selectivity under the existence of EDTA solution,had been successfully applied in the determination of boric acid in natural mineral water for drinking.