In this paper, the influence mechanisms of the solution acidity and the auxiliary electrode reaction on the oxidation peak current of epinephrine (EP) were researched on a pre-anodized carbon paste electrode in a "U" shape electrolytic cell. By changing the solution acidity in the auxiliary electrode electrolytic cell (AEEC) or the working electrode electrolytic cell (WREEC), the electrochemical behaviors of EP in the WREEC was investigated by cyclic voltammetry. It is found that the magnitude of the oxidation peak current of EP is closely related to the solution acidity for both WREEC and AEEC. The effects of the supporting electrolyte, the reduction reaction at the auxiliary electrode, distribution of the EP species and the molecular configuration of EP on the oxidation peak current of EP were also explored. Furthermore, the reaction mechanisms for both cathode and anode were proposed and interpreted. With the provided electrode reaction mechanisms, optimized pH value can be chosen based on the distribution coefficients for future related researches. Satisfactory results have been achieved for the determination of EP in injection using these mechanisms. (C) 2015 Elsevier Ltd. All rights reserved.