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Sulfamethoxazole (SMX) is selected as the research object to investigate the effect of electrocoagulation activation of peracetic acid (EC/PAA) on the degradation of SMX, and the buffering capacity of the EC/PAA system and the mechanism of SMX degradation are also explored. The results show that the EC/PAA system could degrade 96% of SMX within 20 minutes under the optimal experimental conditions as initial pH value of 7, electrolyte Na2SO4 concentration of 50 mmol/L, PAA concentration of 10 mg/L, SMX concentration of 3 mg/L, initial current intensity of 60 mA, and electrode spacing of 2 cm. The coexisting H2O2 and PAA in the solution can produce a synergistic effect with a synergistic coefficient SI of 30.125 0. When the initial pH value of the reaction is between 4 and 8, the pH value can be buffered to around 7 after the reaction, indicating that the system has good pH buffering and electrocoagulation effects; but the degradation of SMX by Fe2+/PAA system is mainly achieved by changing the solution pH, without buffering effect. According to electron paramagnetic resonance (EPR) identification, the active species in the EC/PAA buffer system are mainly • OH, organic free radicals (CH3COO • and CH3COOO •), and ¹O2, with the majority being hydroxyl radical (• OH). These free radicals work together to degrade SMX. [ABSTRACT FROM AUTHOR]