Micromouse competition is an event for self-made maze-solving autonomous robot to competeintelligence and performance. Inspired by this competition, the newly designed small scale soft brake aims to promote the walking performance of the micromouse. In this paper, a new kind of small-scale soft brake using electro-rheological fluid is developed. The structure and working principle are elucidated. Simulations on Matlab and experimental braking torque measurement experiments are conducted to demonstrate the performance of designed electro-rheological brake.