Oxidation of dopamine inside synaptic vesicles has been considered as one of inducements for Parkinson's disease. Dopamine molecules are often oxidized to quinones, making damages to neurotransmission process. Thus, exploring a controllable molecular switch for dopamine oxidation would make great significance in physiology. In this work, a binary homocysteine-dodecanethiol self-assembled monolayers was constructed on gold surface as a specific molecular switch. Scanning electrochemical microscopy was adopted to investigate the switch behavior for dopamine oxidation. The results showed that the molecular switch was at the ON state in a weak alkaline solution and dopamine oxidation would occur. While, the molecular switch was at the OFF state in a weak acidic solution and dopamine oxidation would be cut off. This controllable ON-OFF phenomenon was attributed to charge reversal on the surface of self-assembled monolayer. Then, Density Functional Theory calculation was adopted to calculate the HOMO-LUMO band gap of dopamine-homocysteine cluster. The theoretical calculation exhibited that charge reversal of homocysteine could adjust the energy barrier of dopamine oxidation. This work would offer some contributions to studies of dopamine oxidation in cellular physiology.