This paper concerns anion resins used for purification in air-cooled condenser which are subject to thermal-induced degradation. To study the degradation rate of the process, resin samples were submitted to service conditions (50 to 80°C) in pure water. The degradation rate constants were obtained by measuring the strong base exchange capacity. It discussed the factor water-resin ratio (soak solution and resin quality ratio) affecting the thermal degradation rate. It showed that the rate constants obeyed the Arrhenius principle, and the degradation reaction follows zero-order kinetics well. Strong-base exchange capacity loss rate increases with the rising water-resin ratio. This study indicated thermal resistance of anion resin is significantly affected by temperature and quantity of water which may induce the errors in comparison of experimental results and the actual operation condition.