In this work, the electrodynamic potential E of the sodium bromide (NaBr) solution and tetrabutyl-ammonium bromide (TBAB) solution in the presence of glucoamylase was determined with an ion selective electrode at 278.15, 288.15, and 298.15 K. In addition, the value of activity coefficient of bromide ions at three temperatures was calculated with the Debye-Huckel equation and Pitzer equation. The results showed that the maximum relative error of activity coefficient of bromide ions calculated by the two methods was 8.63%. The activity coefficient of bromide ions in the NaBr solution decreased with increasing molality of NaBr, and the activity coefficients of bromide ion first decreased and then increased with increasing molality of TBAB. The concentration of glucoamylase had different effects on the relationship between the activity coefficient of bromide ions and electrolyte concentration at different temperatures. The value of the activity coefficient of bromide ions in the TBAB solution was greater than that in the NaBr solution at the same temperature.