A new indirect AAS method for the determination of the total amount of acid in soda water is investigated. After adding MgNH4PO4 reagent to sample solution to react with organic acid, the unreacted reagent subsides by using centrifuge and Mg is detected in solution by AAS. The content of acid is calculated in samples. The results agreed weel with those obtained by volumetric analysis. The relative standard deviations are less than 5.3% and the recoveries are between 91 and 104%.