Microfluidic Chip is the main platform of microfluidic technology. The biochemistry reaction on microchip can reduce the consumption of reagent, shorten the reaction time and achieve high throughput. However, the high specific surface area and the interaction between the fluid and the solid wall interface affect the flow in microflow badly. It was shown that hydrophobic surface can produce an effective drag reduction effect. And polydopamine ( PDA ) has the advantages of strong adhesion, good biocompatibility and pH response. So in this work, we photoetched poly-dimethyl siloxane ( PDMS ) by SU-8 gel technique to obtain microflow channel with gradient scale micron scale. Then the polydopamine spheres with particle size of 100 nm were grafted to the microflow channel. After disodged the SU-8 gel, the PDMS was decorated with a layer of polydopamine membrane for hydrophilic modification. Finally a PDMS microfluidic chip with superhydrophobic channel was obtained. The preparation method of this material was simple and the throughput of PDMS microfluidic chip was high. Importantly, the hydrophobicity of the channel is pH responsive. The microstructure and surface morphology of PDMS microfluidic chip were characterized by SEM and AFM. The results show that the flow channel of this material has uniform nanoscale protuberance. The dynamic water contact angle indicates that the hydrophobicity of the channel can change by 50 ° with the change of pH. Keywords: Microfluidic chip; surface modification; polydopamine; pH response