The core of random numbers is the unpredictability and non-repeatability of numbers．It is a key issue in the field of cryptography research and an important guarantee for information security．Based on the randomness of Brownian motion，a device for generating random numbers is designed and fabricated．The device is mainly used as a source for generating random numbers by tracking the trajectory changes of particles doing Brownian motion．using the experimental device to sample 537 sets of data to analyze the generation of random numbers，it is found that the probability of the generated decimal random numbers is basically equal，and the maximum error is only 0．017，which can meet the needs of unpredictability and non-repeatability of true random numbers．