The magneto-rheological fluid brake of electric vehicle is regarded as the research object,the internal structure of the magneto-rheological fluid is analyzed and its structure is optimized,and the theoretical model before and after optimization are established,the relationship between the braking torque and coil current and brake speed and braking time are calculated by Matlab,the experimental method is used to verify the calculation results. The theoretical calculation and experimental results show that there is a large optimization space for the internal structure of magneto-rheological fluid brake,the braking performance of the magneto-rheological fluid braking system can be improved by optimizing the internal structure of the brake,at the same time,it provides an important foundation for the precise control of the electric vehicle brake system,the experimental results and the theoretical calculation results are basically similar to verify the accuracy of theoretical calculation. This research can provide the theoretical basis and important reference for the braking efficiency improvement of electric vehicle and precise brake control.