Abstract: To study the effects of acid, alkali and salt activation methods on the detection of capsaicin by different carbon electrodes, and prepare activated carbon electrode sensors to detect the content of capsaicin in red oil and explore the mechanism. In this work, the glassy carbon electrode and graphite electrode were activated by hydrochloric acid, sodium hydroxide, and phosphate solution respectively. Then, the activated electrodes were used as electrochemical sensors to detect the content of capsaicin in red oil, and the effect of activation conditions on detection performance was studied. Subsequently, the electrochemical detection mechanism of capsaicin was investigated by electrochemical experiments, scanning electron microscopy and Raman spectroscopy. According to the results, activation can significantly enhance the detection sensitivity of the electrode to capsaicin. Among them, phosphate activation method was the best activation method, and the activated graphite electrode showed the best detection performance for capsaicin. The optimum preparation conditions of phosphate activated graphite electrode were as follows: the phosphate concentration was 0.2 mol/L, the pH was 5.0, the potential range was −2.0~2.2 V, and the number of scanning segments was 20. Under this condition, the response current of capsaicin was 11.2 times higher than that before activation, and the reaction process was a redox reaction controlled by diffusion. Additionally, the surface oxygen content of activated graphite electrode increased from 0.8% to 34.9%. The detection mechanism was that capsaicin gains and loses electrons to generate electrical signals, and increases the oxygen containing groups on the electrode surface through phosphate activation to improve the detection sensitivity. The linear range of capsaicin content in red oil obtained by phosphate activated graphite electrode was 5~80 μmol/L, detection limit was 2.30 μmol/L, the recovery rate of spiking was 98.23%~112.60%, the error was less than 10% compared with LC-MS, and the sensor had good anti-interference ability and stability. Using phosphate activated graphite electrode to detect capsaicin content in red oil is simple, economical, and effective, and this method can provide some reference for production practice.