Cyclic voltammetry,IR spectroelectrochemistry,cyclic voltabsorptometry and derivative cyclic voltabsorptometry techniques were used to investigate the electrochemical reduction of tetramethyl-p-benzoquinone(TMBQ) in CH3CN solution.The experimental results showed that the electrochemical reduction of TMBQ is not simple two-step single electron transfer process.Further study indicated that the reduction process is coupled with following chemical reaction.An irresversible oxidation peak at-0.32 V was observed.The result suggests that dimerization reaction occurred during the electrochemical reduction process of TMBQ.In situ IR spectroelectrochemistry further confirmed the formation of dimers.