Three kinds of organic mediators based on arylimidazole (M), triphenylamine (P) and carbazole (C) were synthesized and their electrochemical redox reversibility were characterized through CV. Their redox potentials and electrochemical reversibility were greatly effected by the organic framework of the mediator. The electro-oxidation activity of p-MT under P and C, respectively, were studied through CV and controlled potential electrolysis at room temperature. When 10% H2O was added，the yield of p-MBA was 83% on the electro-oxidation of p-MT under 1mmol/L P at 1.2V. And the excellent electro-catalytic activity and selectivity on the electro-oxidation of p-MBzOH to p-MBA were showed. Compared the activity of P and C on the selectively electro-oxidation synthesis of p-MBA，P with lower redox potential was suit for p-MT with lower oxidation potential, while C with higher redox potential was suit for p-MBzOH with higher oxidation potential.